Seminar Presentations

2018

THz Spintronics in Magnetic Heterosctructures: The Role of Interfaces

Record: VT-12-055
Title: THz Spintronics in Magnetic Heterosctructures: The Role of Interfaces
Authors: Guanqiao Li
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: Radboud University
Date: 2/2/2018
Time: 11:00 AM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: THz spectroscopy provides a convenient way to directly probe the dynamics of photocurrents and spins on the picosecond and sub-picosecond timescale. Recently it was shown that circularly polarized femtosecond laser excitation in a Co/Pt bilayer can effectively generate an ultrafast photocurrent pulse at the interface [1]. The direction of this photocurrent is parallel to the in-plane magnetization of the Co layer and can be controlled by both the magnetic polarity of Co and the chirality of the circularly polarized light. Simultaneously, an ultrafast spin current pulse is generated in the Co layer, which is converted to a charge current in the Pt layer via the inverse Spin-Hall effect [2]. This charge current is in-plane and perpendicular to the magnetization of Co. Moreover, its direction can be controlled by the net spin orientation of the ultrafast spin current by switching the magnetization orientation of Co. A convenient way to probe these ultrafast phenomena is to employ THz time-domain emission spectroscopy. The basic principle of this method is that the (sub)picosecond currents will generate electric radiation in the THz frequency that can be probed via a technique called electro-optical sampling. Since the polarization of THz radiation generated by the two charge currents are perpendicular with respect to each other, one can study each phenomenon separately using wire-grid polarizers. The role of the interfaces between magnetic and non-magnetic layers will be discussed, in particular the generation of the ultrafast photocurrents in Co/ZnO/Pt, Co/Cu/Pt trilayers. The separation of the Co/Pt interface with interlayers of different characteristics is shown to give a better understanding of the role of the interface on the generation of ultrafast photocurrents.
[1] Huisman, T. J., et al. "Femtosecond control of electric currents in metallic ferromagnetic heterostructures." Nature nanotechnology (2016).
[2] Kampfrath, T., et al. “Terahertz spin current pulses controlled by magnetic heterostructures”, Nature nanotechnology (2013).

 

2017

Magnetization Dynamics Triggered by Femtosecond Laser Excitation

Record: VT-12-054
Title: Magnetization Dynamics Triggered by Femtosecond Laser Excitation
Authors: Alexey Kimel
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: Radboud University
Date: 3/15/2017
Time: 11:00 AM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: Femtosecond (fs) laser pulses are among the shortest stimuli in contemporary experimental physics. Controlling the magnetic state of media with ultrashort laser pulses is a rapidly growing research area which promises to revolutionize information processing by achieving the fastest possible and least dissipative magnetic recording [1,2]. The interaction of light with electrons, within the electric-dipole mechanism, conserves the electron spin. As a result, the mechanisms allowing femtosecond optical control of magnetism are among the most heavily debated fundamental questions in contemporary condensed matter research. In my lecture I will review recent progress in the field of femtosecond opto-magnetism. Several examples revealing the ways to boost the susceptibility of magnetic metals and dielectrics to ultrafast optical excitation will be discussed. For instance, the importance of interfaces [3] and domain walls [4] will be emphasized in the case of femtosecond opto-magnetism of Co/Pt multilayers. We will highlight the role of rare-earth ions in the case of effective optical control of magnetism in orthoferrites [5] and the role of doping in the case of photo-magnetic recording in iron garnets [6]. It will be also shown that non-collinear spin structures are more susceptible to femtosecond laser excitation that their collinear counterparts [7].

Ultrafast and Very Small Discover Nanoscale Magnetism with Picosecond Time Resolution Using X-Rays

Record: VT-12-053
Title: Ultrafast and Very Small Discover Nanoscale Magnetism with Picosecond Time Resolution Using X-Rays
Authors: Hendrik Ohldag
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 1/17/2017
Time: 4:00 PM
Room Location: Jack Keil Wolf Auditorium - CMRR Building
Abstract: Today’s magnetic device technology is based on complex magnetic alloys or multilayers that are patterned on the nanoscale and operate at GHz frequencies. To better understand the behavior of such devices one needs an experimental approach that is capable to detect magnetization with nanometer and picosecond sensitivity. In addition, since a device contains different magnetic elements, a technique is needed that provides element specific information about not only ferromagnetic but antiferromagnetic materials as well. Synchrotron based x-ray microscopy provides exactly these capabilities, because a synchrotron produces tunable and fully polarized x-rays with energies between several tens of eV up to tens of keV. The interaction of tunable x-rays with matter is element specific, allowing us to separately address different elements in a device. The polarization dependence or dichroism of the x-ray interaction provides a path to measure a ferromagnetic moment and measure its orientation or determine the orientation of the spin axis in an antiferromagnet. The wavelength of x-rays is of the order of nanometer, which enables microscopy with nanometer spatial resolution. And finally, a synchrotron is a pulsed x-ray source, with a pulse length of tens of picosecond, which enables us to study magnetization dynamics with a time resolution given by the x-ray pulse length in a pump-probe fashion. The goal of this talk is to present an introduction into the field and explain the capabilities of synchrotron based x-ray microscopy to a diverse audience, which is becoming a tool that is available at every synchrotron. The general introduction will be followed by a set of examples that will depend on the audience and range from properties of magnetic materials in rocks and meteorites over magnetic inclusions in magnetic oxides and interfacial magnetism in magnetic multilayer to the dynamics of nanostructured due to field, current pulses as well as microwave excitations.

2016

ZOOMING in on data storage and the HDD

Record: VT-12-052
Title: ZOOMING in on data storage and the HDD
Authors: Roger Wood
Group: Tribology & Mechanics (Talke)
Date: 11/9/2016
Time: 2:00 PM
Room Location: Jack Keil Wolf Auditorium - CMRR Building
Abstract: Get ready for a wild ride starting with the vast distances of outer space and ending with the tiny distances that separate atoms. For a very different perspective on data storage, each slide in the presentation looks at things on a scale that is a factor of ten smaller than the previous slide. The common thread is the technology of information storage. Information storage is what defines human history and it is the machine-readable data storage developed in the last half-century that provides the foundation of the modern information age. More than anything, data storage implies magnetic recording and the hard disk drive. The humble Hard Disk Drive contains such exquisite technologies and operates at such astounding precision that it almost defies belief. Yet, our industry churns out these devices by the hundreds of millions and sells them for a few tens of dollars each. Please enjoy this light-hearted logarithmic romp through storage technology from interstellar space to interatomic spacings. This is a repeat of the talk given in June at the annual ASME ISPS banquet in Santa Clara, California. The talk is non-confidential.

Everything You Wanted to Know About Replication in Industry (but were afraid to ask)

Record: VT-12-051
Title: Everything You Wanted to Know About Replication in Industry (but were afraid to ask)
Authors: Leehod Baruch
Group: Coding & Modulation (Siegel)
Date: 8/12/2016
Time: 2:00 PM
Room Location: Jack Keil Wolf Auditorium - CMRR Building
Abstract: Companies have to protect their valuable data. The loss of data can cause a business damage which can sometimes be quantified with a price tag. This is one of the major considerations in the decision of which data protection method to use. Each method has different properties and requirements from the compute, network and storage infrastructure. A walk through synchronous/asynchronous continuous replication and snapshot based replication flows reveals their characteristic. The implementation details show the engineering challenge in the physical and virtual worlds and the feature richness creates opportunities for new combinations, ideas and innovations.

BiFeO3 for electronics, magnonics, photonics and beyond

Record: VT-12-049
Title: BiFeO3 for electronics, magnonics, photonics and beyond
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 3/8/2016
Time: N/A
Room Location: Jack Keil Wolf Auditorium
Abstract: BiFeO3 is one of the very few room-temperature multiferroic materials. Its rediscovery thirteen years ago was initially motivated by a possible application in electric-field controlled spintronics devices. Other important properties of BiFeO3 are its remarkable spontaneous polarization of 100microC/cm2 in the <111> pseudocubic direction, high Curie temperature of 1100 K and cyclodial spin order in the bulk. In addition BiFeO3 exhibits interesting optical characteristics, such as a band gap in the visible range (2.7eV) and a large birefingence.

Materials Challenges for Next-Generation, High-Density Magnetic Recording: Media and Read Heads

Record: VT-12-045
Title: Materials Challenges for Next-Generation, High-Density Magnetic Recording: Media and Read Heads
Authors: Kazuhiro Hono
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 1/11/2016
Time: 11:00 AM
Room Location: Jack Keil Wolf Auditorium
Abstract: The hard disk drive industry is making continuous efforts to increase the areal density of magnetic recording. To realize an areal density of higher than 2 Tbit/in2 in the future, both media and readers need technical breakthroughs. Since the bit size will be in the range of 20 nm, the magnetic grains in the recording media must be reduced to less than 6 nm, requiring the use of ferromagnetic materials with high magnetocrystalline anisotropy such as L10 FePt. The shield-to-shield spacing of read sensors must also be smaller than 20 nm with low device resistance (resistance-area product RA ? 0.5 ? ?m2), which is very difficult to achieve using MgO based tunneling magnetoresistance devices. In this talk, we will address the materials challenges to the realization of an ideal media nanostructure using L10 FePt for heat-assisted magnetic recording (HAMR) media and narrow readers for > 2 Tbit/in2 areal density. Recently significant progress has been made in current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) devices using highly spin-polarized Heusler alloy ferromagnetic layers and new spacer materials. The very high magnetoresistance ratios achieved in CPP-GMR are encouraging for future read head applications of CPP-GMR, or its laterally extended version, lateral spin valves. The devices with high magnetoresistive output at low RA may open new applications in addition to disk read heads.

2015

Erasure-Correcting Codes with Local and Global Properties

Record: VT-12-046
Title: Erasure-Correcting Codes with Local and Global Properties
Authors: Mario Blaum
Group: Coding & Modulation (Siegel)
Date: 11/20/2015
Time: 2:00 PM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: A lot of interest has arisen in recent literature on erasure-correcting codes having local and global properties. For example, assume that we have a number of storage devices. The most common way to protect against a device failure is by using the so called RAID 5 architecture, which consists on assigning a parity device, then the contents of any failed device can be retrieved by simply XORing the contents of the surviving devices. However, there are situations in which one or more sectors within the surviving devices experience a failure (a common occurrence in flash memories that decay in time). In that case, data loss will occur. Certainly, it is possible to increase the number of parity devices, like in RAID 6, that uses two parity devices. However, these solutions are expensive, so situations where the use of a couple of extra parity (global) sectors that can take care of situations like this will be explored. Specifically, the use of a few sectors for local correction and invocation of some global parities and all the sectors in the array for more infrequent situations is desired. That way, the data loss situations mentioned above are avoided. Some popular codes with local and global properties are Local Redundancy Codes (LRC), which optimize the minimum distance given the constraints of the problem, Partial MDS codes (PMDS), which optimize the erasure-correcting power of the code given the number of extra global parity symbols, and Sector Disk codes (SD), which are weaker than PMDS codes but focus on the failure mode involving whole device and random sectors, when the devices are preferably flash memory devices. These schemes are going to be reviewed, with some detailed description of PMDS codes. Open problems and questions are going to be mentioned.

Magnetic Nanowires: Revolutionizing Hard Drives, RAM, and Cancer Treatment

Record: VT-12-041
Title: Magnetic Nanowires: Revolutionizing Hard Drives, RAM, and Cancer Treatment
Authors: Bethanie Stadler
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 11/16/2015
Time: 11:00 AM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: Magnetic nanowires can have many names: bits, sensors, heads, artificial cilia, sensors, and nano-bots. These applications require nanometer control of dimensions, while incorporating various metals and alloys. To realize this control, our 7- to 200-nm diameter nanowires are synthesized within insulating matrices by direct electrochemistry, which negates sidewall damage such as that caused by lithographical patterning of vacuum-deposited structures. Our nanowires can easily have lengths 10,000x their diameters, and they are often layered with magnetic (Co, Fe, FeGa, FeNi, Ni) and non-magnetic (Ag, Cu, Au) metals as required by each application. This talk will reveal synthesis secrets for nm-control of layer thicknesses, even for difficult alloys, which has enabled studies of magnetization reversal, magneto-elasticity, giant magnetoresistance (GMR), and spin transfer torque (STT) switching. In addition, this lithography-free synthesis yields 10-nm diameter nanowires that have resistivities of only 5.4mW.cm (nearly that of bulk copper) due to negligible sidewall roughness. Therefore, these nanowires will mitigate the ITRS Roadmap’s “Size Effect” Grand Challenge which identifies the high resistivities in small interconnects as a barrier to continued progress along Moore’s Law (or better). Ten-nm diameter trilayers of [Co(15nm)/Cu(5nm)/Co(10nm)] have also met or surpassed all of the criterion for the world’s smallest read heads with 30 O resistance and 19% magnetoresistance. High magnetoresistance is also possible in other multilayered nanowires that exhibit excellent properties for mulit-level nonvolatile random access memory (RAM) using STT switching at very low current densities (100kA/cm2). If the insulating growth matrix is etched away, the nanowires resemble a magnetic bed of nano-seaweed which enables microfluidic flow sensors and vibration sensors. Finally, we have incubated various nanowires with several healthy and cancerous cell lines, and find that they are readily internalized by all cell types thus far. Careful magnetic design of these “nano-bots” enables external steering, nano-barcode identification, and several modes of therapy. In short, by the end of this talk, I hope you will be convinced that magnetic nanowires can and will revolutionize hard drives, RAM, and cancer treatment.

Theory of Codes in Network and Interference Problems

Record: VT-12-049
Title: Theory of Codes in Network and Interference Problems
Authors: Arya Mazumdar, Manuel Bibes
Group: Coding & Modulation (Siegel)
Date: 11/6/2015
Time: 11:00 AM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: Due to applications in large-scale distributed storage systems, local encoding and repair properties of codes have recently earned a lot of attention. In the first part of the talk, we show that generalized locality properties of codes lead to the notion of a graph capacity that is fundamental in the study of network flow problems. Furthermore, this capacity is closely related to the steady-states of graph dynamical systems, and thus steer us towards applications in neural auto-associative memories and consensus-based community detection algorithms. In the second part of the talk we will address another general application of codes motivated by the pseudo-random behavior of code-words distribution. We will show how this basic principle is used to provide deterministic construction of structured matrices for applications such as sparse recovery and low-rank approximation.

Areal Density Limits of Magnetic Recording and Drive Architecture

Record: VT-12-048
Title: Areal Density Limits of Magnetic Recording and Drive Architecture
Authors: Kai-Zhong Gao
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 10/28/2015
Time: 2:00 PM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: Recent high areal density capability (ADC) demonstration of heat assisted magnetic recording (HAMR) has shown a high effective field gradient can be achieved in the write process, and the ADC for HAMR is comparable to conventional perpendicular magnetic recording (PMR) [1, 2]. As the recording track density increases, the normalized curvature, as seen by the read head, also increases. A study of the read and write processes for HAMR and perpendicular recording have shown that the smallest (1T) bit width is rapidly reduced as the linear density of the recording system exceed beyond 2000kbpi. This reduction of small bit width at high linear density is mainly due to the reduction of gradient at the off track position and the large curvature, which further reduce the linear density capabilities. The same phenomenon can be observed in both HAMR and PMR systems [3]. The results are in good agreement with experiments [1,2]. Although the read head width is wide, the demonstration still prefers narrow dimension for both read and write elements. Shingled magnetic recording was implemented to extend magnetic recording ADC for PMR product [4]. While the HDD industry is trying to implement assisted technology such as HAMR, continue extending ADC for PMR before assisted technology ready for product is crucial for HDD industry. As the areal density growth rate for the recording industry slows down, every percentage (%) of ADC increase become more important than ever. Some improvements have been proposed recently to further improve the ADC on or beyond SMR, here we show a new drive architecture that enables an additional drive capacity increase for a given choice of head and media, as compare to conventional and SMR recording. We show that this approach can be easily implemented and will further extend the ADC for both PMR and assisted magnetic recording technologies [5].

Giant Magnetoresistance in Magnetic Nanostructures: A Unified View on Granular and Multilayer Systems

Record: VT-12-043
Title: Giant Magnetoresistance in Magnetic Nanostructures: A Unified View on Granular and Multilayer Systems
Authors: Imre Bakonyi
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 10/16/2015
Time: 11:00 AM
Room Location: Jack Keil Wolf Auditorium
Abstract: In the last two decades, a lot of efforts have been devoted to studies of the giant magnetoresistance (GMR) effect in electrodeposited multilayer films which field has been reviewed recently. We have presented experimental results which enabled us to reveal that the commonly observed strongly non-saturating behaviour of the field-dependence of the GMR in these systems originates from the presence of superparamagnetic (SPM) regions in the magnetic layers. More recently, we have identified a physical model elaborated originally for granular metals and could be well adapted for the case of electrodeposited multilayers. A new procedure has also been presented how to separate the SPM contribution to the GMR from the conventional ferromagnetic GMR contribution. This represents a significant progress in understanding the underlying physical processes. In the present contribution, we intend to give a description of the spin-dependent scattering processes occurring in various magnetic nanostructures which form the basis for explaining the phenomenon of GMR. The two limiting cases are (i) classical granular metals in which nanoscale non-interacting ferromagnetic (FM) particles with SPM characteristics are embedded in a non-magnetic matrix and (ii) perfect nanoscale metallic multilayers in which FM layers are separated by non-magnetic layers. In the first case, the field dependence of the magnetoresistance is proportional to the square of the Langevin function L(x) describing the field dependence of the magnetization where x = ?H/kT with ? as the average SPM particle moment. In perfect multilayers, the field dependence of the GMR is governed by the interplay between the coupling between the FM layers via the non-magnetic spacer layers and the magnetic anisotropy. Besides the general overview of spin-dependent transport processes in ideal and non-ideal magnetic nanostructures, we also present our recent theoretical results for the field dependence of the GMR in the case of antiferromagnetic and/or orthogonal coupling in the absence of any magnetic anisotropy. The talk will also give a brief description of the preparation of multilayers by electrodeposition and present our main results on their GMR behaviour. More details about electrodeposited multilayers can be found in our recent review.

Interaction of Ferromagnetics and Superconducting Permanent Magnets - Superconducting Levitation

Record: VT-12-044
Title: Interaction of Ferromagnetics and Superconducting Permanent Magnets - Superconducting Levitation
Authors: Ludwig Schultz
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 10/16/2015
Time: 4:00 PM
Room Location: Jack Keil Wolf Auditorium
Abstract: New means of urban transportation and logistics will become realistic with superconducting magnetic bearings using bulk high temperature superconductors. The advantage of super¬con-ducting magnetic levitation is that it works passively stable without any electronic control but with attracting and repelling forces to suspend a vehicle pendant or standing upright from zero to high speed - perfect conditions for the idea of rail-bound individual transport with cabins for 4 - 5 passengers requested call by call. They will levitate noiseless over the track made of RE permanent magnets saving energy and travel time. A big step forward to this vision has been made in Dresden. The world largest research and test facility for transport systems using HTS bulk material in the levitation and guidance system in combination with a permanent magnet track was put into operation. A vehicle for 2 passengers, equipped with linear drive propulsion, non-contact energy supply, second braking system and various test and measurement systems is running on an 80 m long oval driveway. In the presentation the principle of superconducting levitation by flux pinning in high temperature supercon¬ductors will be described. Based on this an overview of the SupraTrans II research facility and future directions of super¬conductivity-based magnetic levitation and bearing for automation technology, transportation and medical treatment under enhanced gravity will be given.

Coding for the l-Limited Permutation Channel

Record: VT-12-046
Title: Coding for the l-Limited Permutation Channel
Authors: Eitan Yaakobi
Group: Coding & Modulation (Siegel)
Date: 10/2/2015
Time: 11:00 AM
Room Location: Jack Keil Wolf Auditorium
Abstract: In this work we consider the communication of information in the presence of synchronization errors. Specifically, we consider permutation channels in which a transmitted word x = (x1,…,xn) is corrupted by a permutation ? ? Sn (the set of all permutations on n elements) to yield the received word y = (y1,…,yn) where yi = x?(i). We initiate the study of worst-case (or zero-error) communication over permutation channels that distort the information by applying permutations ? which are limited to displacing any symbol by at most r locations, i.e. permutations ? with weight at most r in the l?-metric. We present direct and recursive constructions, as well as bounds on the rate of such channels for binary and general alphabets. Specific attention is given to the case of r = 1. A list of interesting open problems in this area will be given. This is a joint work with Michael Langberg from State University of New-York at Buffalo and Moshe Schwartz from Ben-Gurion University of the Negev.

All-Optical Control of Magnetism: From Fundamentals to Nanoscale Engineering

Record: VT-12-042
Title: All-Optical Control of Magnetism: From Fundamentals to Nanoscale Engineering
Authors: Theo Rasing
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 9/21/2015
Time: 11:00 AM
Room Location: Jack Keil Wolf Auditorium
Abstract: From the discovery of sub-picosecond demagnetization almost two decades ago to the more recent demonstration of magnetization reversal by a single 40 femtosecond laser pulse, the manipulation of spins by ultra short laser pulses has become a fundamentally challenging topic with a potentially high impact for future spintronics, data storage and manipulation and quantum computation. The realization that femtosecond laser induced all-optical switching (AOS) as observed in ferrimagnets exploits the antiferromagnetic exchange interaction between their sublattices, opens the way to engineer new magnetic materials for AOS. Because their dynamics is governed by the exchange interaction, antiferromagnetic materials give rise to the fastest dynamics and, by proper choice of materials, can also lead to very low energy requirements for switching. Another challenge is how to bring the optical manipulation of magnetic media to the required nanoscale, which may be possible using plasmonic or wave-shaping techniques. Recent results with engineered hybrid magnetic materials and nanofocusing will be discussed, showing the practical potential of AOS.

Racing Domain Walls and Laser-Induced Spin Currents

Record: VT-12-040
Title: Racing Domain Walls and Laser-Induced Spin Currents
Authors: Bert Koopmans
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 4/9/2015
Time: 11:00 AM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: Abstract: Novel schemes for controlling magnetization dynamics involving the explicit use of spin-orbit coupling and/or spin transfer phenomena in ultrathin layered magnetic structures have received a boosting interest recently. Apart from confronting researchers with exciting, new physics, entirely novel scenarios for memory and logic devices have been proposed. In this presentation two apparently diverse topics will be addressed: (1) current-induced domain wall motion in ferromagnetic nanoconduits with perpendicular magnetic anisotropy (PMA), and (2) ultrafast laser-induced magnetization dynamics in nanoscaled structures. Both display an intriguing interplay between spin orbit interation and spin-transfer phenomena. In part (1) I will address recent progress in current-induced domain wall motion. It has been found that in magnetic ‘racetracks’ with perpendicular magnetic anisotropy (PMA) extremely high velocities of close to 1000 m/s can be established by a combination of the spin Hall effect and the so-called Dzyaloshinskii-Moriya Interaction (DMI) s. Some of the breakthrough experiments as well as some of our present efforts aiming at engineering the DMI will be discussed. In part (2) I will discuss the competition between local dissipation of angular momentum and laser-induced spin currents in experiments on laser-induced ultrafast magnetization dynamics. A new all-optical approach to disentangle the laser-induced dynamics in multilayer magnetic structures will be introduced. An application to fs laser-induced dynamics in a tri-layer Fe/Ru/Ni structure will be discussed. Furthermore, laser-induced spin transfer torque on a free magnetic layer, using a non-collinear configuration of two magnetic thin films will be demonstrated, and its origin will be discussed. Biography: Professor Bert Koopmans graduated from the University of Groningen, where he also obtained his PhD degree on optical second harmonic generation and fullerenes (1993). After a short stay as a postdoc at the Radboud University Nijmegen, he spent three years as a Humboldt Fellow at the Max-Planck Institute for Solid State Physics in Stuttgart, working on optics of semiconductor quantum structures. In 1997 he joined the Department of Applied Physics at the Eindhoven University of Technology, where since 2003 he is full-professor and Group leader of the Group Physics of Nanostructures (FNA). In 2004 he was awarded a NWO Vici Laureate on a program entitled “Spin Engineering in Molecular Devices”. His current research interests encompass spintronics (including spin transfer and spin-orbit phenomena, domain wall devices and organic spintronics), nanomagnetism and ultrafast spin dynamics. As of 2014 he is in the management team of the Research Centre for Integrated NanoPhotonics, facilitated by a 20 M€ NWO Gravity grant, and where he initiates research on integrated spintronic-photonic memories. At present, he is coordinator of the center for NanoMaterials (cNM) and program director of the Program on Advanced NanoElectronic Devices within NanoNextNL, a national consortium for research on nanotechnology in The Netherlands. Moreover, he is a member of the board of NanoLabNL, a Dutch national facility providing an open-access infrastructure for R&D in nanotechnology, as well as the advisory board of NanoLab@TU/e.

Spintronics without magnet-The Chiral Induced Spin Selectivity (CISS) Effect

Record: VT-12-038
Title: Spintronics without magnet-The Chiral Induced Spin Selectivity (CISS) Effect
Authors: Ron Naaman
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 4/7/2015
Time: 11:00 AM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: Spin based properties, applications, and devices are commonly related to magnetic effects and to magnetic materials. However, we found that chiral organic molecules act as spin filters for photoelectrons transmission, in electron transfer, and in electron transport. The effect introduces the ability to utilize quantum mechanical phenomena at room temperature. The new effect, termed Chiral Induced Spin Selectivity (CISS) has interesting implications for the production of new types of spintronics devices like spin filters and memory and it introduce spin as a possible important parameters in electron transfer in biology. The basic effect, and its applications and implications will be presented

MATLAB Seminar at UCSD - Top 10 Productivity Tools in MATLAB

Record: VT-12-039
Title: MATLAB Seminar at UCSD - Top 10 Productivity Tools in MATLAB
Authors: Sumit Tandon
Group: Tribology & Mechanics (Talke)
Date: 4/7/2015
Time: 3:00 PM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: Please join the Center for Magnetic Recording Research and MathWorks for a complimentary MATLAB seminar hosted by CMRR. Faculty, staff, researchers and students are all welcome to attend. MATLAB is a high-level language and interactive environment for data analysis, visualization, and numerical computation. Using MATLAB, you can reach solutions faster and easier than with spreadsheets or traditional programming languages, such as C/C++ or Java. In this technical session, we present and discuss ways to increase your productivity and effectiveness using MATLAB. We demonstrate and share best practices for exploring, analyzing and visualizing your data, and how to quickly develop algorithms and share results with your colleagues.

Topological protection of magnetic domain walls

Record: VT-12-037
Title: Topological protection of magnetic domain walls
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 3/2/2015
Time: N/A
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: The broken inversion symmetry at ferromagnetic interfaces offers new ways to manipulate the magnetic state. The combination of a heavy metal and a thin ferromagnetic film gives rise to new phenomena which normally vanish in bulk, but play an important role as soon as the thickness of the ferromagnet is reduced to an atomic size. The presence of a Rashba electric field and Dzyaloshinskii-Moryia interaction (DMI) has been recently demonstrated in ferromagnet/heavy metal systems. In this seminar I will talk about the ways to measure the DMI in thin magnetic films macroscopically. Magnetic domain walls are ideal objects for this since they are the first precursors indicating the presence of the DMI. We use magnetic field induced domain wall displacement measurements employing the Kerr microscopy. I will also show that the Néel texture of the magnetic domain walls, which is a consequence of a week DMI, can be revealed by the high resolution Lorentz transmission electron microscopy.

Ferroelectrics: Old Technology with a Thousand New Uses

Record: VT-12-036
Title: Ferroelectrics: Old Technology with a Thousand New Uses
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 2/17/2015
Time: 3:30 PM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: Joseph T. Evans, Jr. is the founder of Radiant Technologies Inc. Radiant has established international standards for electrical evaluation of ferroelectric materials of all types and Radiant continues to sell the most sophisticated test equipment for these materials and their applications. Mr. Evans graduated first in his class in Electrical Engineering from the Air Force Academy in 1976. After pursuing a career as a jet Instructor Pilot, Mr. Evans completed his graduate work in lasers, control theory, and semiconductor fabrication at Stanford University. He then joined the Air Force Weapons Laboratory in Albuquerque, New Mexico.

2014

Engineering Interface Magnetism and Transport via Defect Ordering in Complex Oxide Heterostructures

Record: VT-12-033
Title: Engineering Interface Magnetism and Transport via Defect Ordering in Complex Oxide Heterostructures
Authors: Chris Leighton,Satoshi Okamoto
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: Dept. of Chemical Engineering and Materials Science, University of Minnesota
Date: 12/8/2014
Time: 11:00 AM
Room Location: CMRR Auditorium
Abstract: The remarkable functionality of complex oxides provides many opportunities for new science and applications in oxide heterostructures. The manganite and cobaltite materials crystallizing in the perovskite structure provide excellent examples, being of interest in solid oxide fuel cells, catalysis, gas separation, ferroelectric RAM, resistive switching memory, and oxide electronics/spintronics. However, the same delicate balance between phases that provides such diverse functionality also leads to a serious problem: the difficulty of maintaining desired properties (such as high spin polarization) close to the interface with other oxides, i.e. the “dead layer” problem. Although this appears universal, and presents a significant roadblock to heterostructured devices for oxide electronics/spintronics, there is no consensus as to its origin. In this work, using SrTiO3/La1-xSrxCoO3 as a model system (i.e. a non-magnetic semiconductor / ferromagnetic metal interface), we have determined the fundamental origin of the deterioration in interfacial transport and magnetism. The effect is due to nanoscopic magnetic inhomogeneity near the interface, driven by depletion in hole doping due to accumulation of oxygen vacancies. This occurs due to a novel mechanism for accommodation of lattice mismatch based on formation and long-range ordering of oxygen vacancies. With this understood we demonstrate how interfacial magnetic and electronic properties can be fine-tuned by manipulating oxygen vacancy ordering using strain and crystallographic orientation. The result is a massive suppression in dead layer thickness, an important advance for heterostructured oxide devices. Other surprising results, such as oxygen vacancy order-enhanced anisotropic magnetoresistance, will also be touched upon. Work supported primarily by DOE and NSF.

Focused Electron Beam Induced Deposition (FEBID) fabrication of nano-magnets

Record: VT-12-034
Title: Focused Electron Beam Induced Deposition (FEBID) fabrication of nano-magnets
Authors: Andreas Berger
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: CIC nanoGUNE Consolider, Tolosa Hiribidea 76, San Sebastian-Donostia, Spain
Date: 11/12/2014
Time: 11:00 AM
Room Location: CMRR Auditorium
Abstract: During the past decade, FEBID has been established as a one-step technique for the fabrication of 1-, 2- and even 3-dimensional nanostructures. Specifically, there has been a growing interest in the development of FEBID processes for magnetic materials in the last few years, namely for Fe, Co and Ni [1], which may provide new routes for the fabrication of magnetic nano-devices as well as complex nano-magnet designs. Among these ferromagnetic metals, Co attracts the most attention because an exceptionally high purity can be obtained under the correct deposition conditions. Here, we present a systematic investigation of the deposition parameters and the characterization of the structure and physical properties of our FEBID cobalt deposits, including the effect of unintended parasitic deposits as well as strategies for their removal [2]. The magnetic properties of our deposits were characterized by Magneto-optical Kerr effect (MOKE) microscopy. Specifically, we investigated individual nano-scale wires down to diameter sizes of 30 nm [3] as well as magnetic dot-arrays with periods as low as 13 nm. References [1] R. Lavrijsen et al., Nanotechnology 22, 025302 (2011); O. Idigoras et al., Nanofabriction 1, 23 (2014) [2] E. Nikulina, O. Idigoras, J. M. Porro, P. Vavassori, A. Chuvilin and A. Berger, Appl. Phys. Lett. 103, 123112 (2013) [3] E. Nikulina, O. Idigoras, P. Vavassori, A. Chuvilin and A. Berger, Appl. Phys. Lett. 100, 142401 (2012)

Silicon Spintronics

Record: VT-12-033
Title: Silicon Spintronics
Authors: Ron Jansen
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: AIST, Tsukuba, Japan
Date: 10/30/2014
Time: 11:00 AM
Room Location: CMRR Auditorium
Abstract: Worldwide efforts are underway to create a revolutionary and energy-efficient information technology in which digital data is represented by the spin orientation of electrons. Implementing spin functionality in silicon, the mainstream semiconductor, has the potential to create broad impact. Remarkable advances in the creation and control of spin polarization in silicon have therefore generated much excitement. This lecture provides a transparent picture of silicon spintronics, including the key developments and achievements, our current understanding, as well as the unsolved puzzles and challenges that stimulate researchers in the field. First, the basic idea of spin-based information technology and silicon spintronics is introduced. Ferromagnets have non-volatile memory func¬tionality, whereas semiconductors provide amplification and transis¬tor action. What if we integrate ferromagnets and silicon — magnetic memory and logic computing? Then the main building blocks are described: one needs to be able to create spin polarization in the silicon, to manipulate it, and thereafter detect the spins. The generation of a spin flow by electrical means (driven by a bias voltage) or thermal means (driven by a heat flow) are discussed. Ferromagnetic tunnel contacts are shown to provide a robust method to do this, at room temperature. The lecture concludes with a prospect on future developments, which certainly includes more surprises as silicon spintronics comes of age. [1] R. Jansen, Silicon spintronics, Nature Materials 11, 400-408 (2012). [2] J.C. Le Breton, S. Sharma, H. Saito, S. Yuasa and R. Jansen, Thermal spin current from a ferromagnet to silicon by Seebeck spin tunnelling, Nature 475, 82-85 (2011). [3] S.P. Dash, S. Sharma, R.S. Patel, M.P. de Jong and R. Jansen, Electrical creation of spin polarization in silicon at room temperature, Nature 462, 491-494 (2009).

Nano-Spintronic Devices

Record: VT-12-032
Title: Nano-Spintronic Devices
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 10/29/2014
Time: 2:00 PM
Room Location: Jack Keil Wolf Auditorium (formerly known as CMRR auditorium)
Abstract: Recent advancement in nanofabrication and growth allows the utilisation of spin-polarised electrons in transport and dynamics, resulting in the development of spintronic devices [1]. In the spintronic devices, the key technologies are injection, manipulation and detection of spin-polarised electron in a non-magnetic media with high efficiency. Conventionally such a spin-polarised electron current has been injected into a non-magnetic material by flowing an electrical current through a ferromagnetic layer. However, its spin polarisation is dependent upon the interfacial properties, such as conductance matching, junction resistance and interfacial resonant states. We recently succeeded to fabricate an abrupt Fe/GaAs(001) interface for the first time and have demonstrated reproducible spin transport across the interface [2]. This system offers an ideal junction to form a spin-polarised field effect transistor for example. In a lateral spin-valve, such injected spin-polarised electrons diffusively travel in a non-magnetic media. This reduces the efficiency of the device operation. We recently proposed a geometrical ratchet effect to amplify the spin-polarised electron currents in such a device [3]. By optimising the geometry we achieved about 7 times amplification as compared with a conventional straight-wire device. By utilising these fundamental building blocks, we can also develop a large variety of new devices. This work was partially supported by the EPSRC (EP/I000933/1 and EP/K03278X/1), Royal Society Industry Fellowship, EC (NMP3-SL-2013-604398) and JST-PRESTO. [1] A. Hirohata and K. Takanashi, J. Phys. D: Appl. Phys. 47, 193001 (2014). [2] L. R. Fleet et al., Phys. Rev. B 87, 024401 (2013). [3] R. M. Abdullah et al., J. Phys. D: Appl. Phys. (in press).

Topological Effects in Nanomagnetism: From Perpendicular Recording to Monopoles

Record: VT-12-030
Title: Topological Effects in Nanomagnetism: From Perpendicular Recording to Monopoles [IEEE]
Authors: Hans-Benjamin Braun
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: School of Physics, University College Dublin, Ireland
Date: 10/13/2014
Time: 11:00 AM
Room Location: CMRR Auditorium
Abstract: Similar to knots in a rope, the magnetization in a material can form par- ticularly robust configurations. Such topologically stable structures include domain walls, vortices and skyrmions which are not just attractive candidates for future data storage applications but are also of fundamental importance to current memory technology. For example, the creation of domain wall pairs of opposite chirality delimits the thermal stability of bits in present high anisotropy perpendicular recording media. The ever increasing demand for higher data storage density forces us to understand topological defects at ever decreasing length scales where thermal and quantum effects play an increasingly important role. This talk will be adapted to the interests of the audience and will start with an overview over topological defects in magnetic systems. As a practical ap- plication it is shown how thermal domain wall nucleation affects the design of perpendicular magnetic recording media. In a second part, it is demonstrated how the geometric Berry’s phase allows micromagnetics to be extended to include quantum effects. As an important consequence it will be shown how the chirality of a classical domain wall translates into quantum spin currents which in turn can be used for infor- mation transport. All concepts will be illustrated by state of the art experiments, which encompass the techniques of polarized neutrons and synchrotron x-rays. The final part of the talk will discuss how magnetic monopoles emerge as topological defects in densely packed arrays of nanoislands which effectively interact as dipoles, a system also known as ‘artificial spin ice’. In contrast to conventional thin films, where magnetization reversal occurs via nucleation and extensive domain growth, magnetization reversal in 2D artificial spin ice is restricted to an avalanche-type formation of 1D strings. These objects constitute classical versions of Dirac strings that feed magnetic flux into the emergent magnetic monopoles. It is demonstrated how the motion of these magnetic charges can be individually controlled experimentally and used to perform simple logic operations. [1] H.B. Braun, "Topological e ffects in nanomagnetism: from superparamagnetism to chiral quantum solitons", Adv. Phys. 61, 1-116 (2012). [2] E. Mengotti, L.J. Heyderman, A. Fraile Rodriguez, F. Nolting, R.V. Hugli, and H.B. Braun, "Real space observation of Dirac strings and magnetic monopoles in articial kagome spin ice", Nat. Phys. 7, 68 (2011).

Microwave assisted magnetization switching on perpendicular magnetic nano-scale elements

Record: VT-12-025
Title: Microwave assisted magnetization switching on perpendicular magnetic nano-scale elements
Authors: Satoshi Okamoto
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 10/9/2014
Time: 4:00 PM
Room Location: CMRR Auditorium
Abstract: Microwave assisted magnetization recording (MAMR) has attracted much attention as one of the prospective future recording technologies. In MAMR, the field required for magnetization switching can be significantly reduced by applying radio-frequency magnetic fields. The microwave assistance effect is not only the technology which simply reduces the switching field of the media but also the one controls the precessional motion of the magnetization. In this sense, the microwave assistance effect is qualitatively different from the conventional recording technology and also the other future technologies such as BPM and HAMR. Therefore, control of the precessional motion may open a way for the new recording architectures such as 3D recording, which are hardly realized in the framework of conventional recording system. In this talk, I will present the basic theory of microwave assistance effect and compare the experimental results using the perpendicular magnetic Co/Pt multilayer nanodots and the CoCrPt based granular film.

Magnetic Materials in Medicine: Applications in Diagnosis, Management, and Treatment of Disease

Record: VT-12-027
Title: Magnetic Materials in Medicine: Applications in Diagnosis, Management, and Treatment of Disease
Authors: Tim St. Pierre
Group: Magnetic Materials Design and Fabrications (Jin)
Affiliation: School of Physics, The University of Western Australia
Date: 9/8/2014
Time: 11:00 AM
Room Location: CMRR Auditorium
Abstract: Scientists working in the field of magnetic materials are increasingly focusing their attention on new applications of magnetic detection and magnetic transduction techniques in the biomedical sciences. Iron is a key functional element in the human body and surpasses all other naturally occurring elements in the body in terms of both the variety and magnitudes of its magnetic states. In many diseases, the quantity and the magnetic state of iron are altered by the disease. Hence, detecting and measuring the magnetic properties of the iron in vivo or in samples of body fluids can give insights into the state of health of a human subject. Example applications include assessing the risk of organ damage in hereditary hemochromatosis [1], determining the dose of iron chelator drugs required for patients with thalassemia [2], and identifying infectious forms of the malarial parasite in finger-prick blood samples [3]. Scientists are also working on the development of synthetic magnetic particles that can be injected into the human body for the diagnosis and treatment of disease. The particles used are generally in the size range of 10 to 100 nm. They can be used to enhance the contrast in magnetic resonance images to help identify tumors in tissue [4], to act as local heat sources to treat cancer [5], and to carry, concentrate, and release drugs more specifically than drugs without a magnetic carrier [6]. In this presentation, the physical and chemical principles behind these biomedical applications and their impact on medicine will presented at a level suitable for a generalist audience.

Optical control of magnetism beyond the light-diffraction limit in rare- earth/transition metal samples

Record: VT-12-026
Title: Optical control of magnetism beyond the light-diffraction limit in rare- earth/transition metal samples
Authors: Matteo Savoini
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 8/22/2014
Time: 11:00 AM
Room Location: Center for Magnetic Recording Research Auditorium
Abstract: The interaction of sub-picosecond laser pulses with magnetically ordered materials has developed into a fascinating research topic in modern magnetism. From the discovery of sub-picosecond demagnetization over a decade ago to the recent demonstration of magnetization reversal by a single 40 fs laser pulse, the manipulation of magnetic order by ultrashort pulses has become a fundamentally challenging topic with a potentially high impact for future spintronics, data storage and manipulation [1]. This has firstly been observed in rare-earth/transition metal amorphous alloys, but recently all-optical switching has been demonstrated in multilayer structures [2] and even in rare-earth free ferromagnetic compounds [3], this implying that it is a more general effect than previously anticipated. A couple of fundamental questions need to be addressed before being able to exploit this effect in real applications: which is the ultimate spatial resolution achievable and how does the sample structure (amourphous alloy VS multilayer structure VS rare-earth free samples) influence the ultimate reversal speed? Here I present results on the magnetization control at the sub-100 nm level using plasmonic nano-antennas. In fact, all-optical switching of domains as small as 40 nm in diameter has been achieved thanks to the field confining effects of resonant dipolar antennas [4]. Moreover, preliminary results on the switching dynamics in samples other than amorphous alloys will be presented. In particular we find that it is possible to optically switch in- and out-of-plane samples composed by multilayer structures of Gd and FeCo, with switching rate comparable to those measured in amorphous alloys; but we are also able to drive the reversal process along different routes playing with an external magnetic field [5]. [1] A. Kirilyuk, et al., Rev. Mod. Phys. 82, 2731 (2010). [2] S. Mangin, et al., Nature Materials 13, 286 (2014). [3] C.-H. Lambert, et al., arXiv:1403.0784 (2014) [4] T.M. Liu, et al., in preparation. [5] M. Savoini, et al., submitted.

Effectively Manipulating the Magnetic State of a Ferromagnet

Record: VT-12-025
Title: Effectively Manipulating the Magnetic State of a Ferromagnet
Authors: Jon Gorchon
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 7/21/2014
Time: 11:00 AM
Room Location: Auditorium
Abstract: Effectively manipulating the magnetic state of a ferromagnet has a great interest for possible technological applications. Understanding the underlying fundamental mechanisms is thus particularly important. In some cases, the understanding of some mechanisms may even importantly impact other areas of physics. This is the case for example with field induced magnetic domain walls motion in the creep regime, where the wall can be assimilated to an elastic interface and follows an universal behaviour This thesis presents through an experimental work on Pt/Co/Pt ultra-thin samples, a complete description of the temperature and field dependent domain wall dynamics. A self-consistent analysis allows the extraction of all control parameters, identifying the new Thermally Activated Flux Flow regime, and confirming universal thermal scaling exponents. A second study focuses on current induced domain wall motion in an extended geometry of a (Ga,Mn)(As,P) ferromagnetic film. This study unveils domain wall shape instabilities under a gradient of current. The instability limits are analytically predicted in agreement with the experimental observations. A third work concerns the magnetization reversal mechanism evidenced at the interface between a (Ga,Mn)(As,P) film and a non-ferromagnetic electrode under a current flow. The reversal is shown to be stochastic and mainly governed by the spin accumulation at the interface, which reduces importantly the local magnetization. A simplified model allows the description of the reversal probability and the time scales involved in the mechanism of reversal are accessed and discussed.

STT-MRAM: Past, Present, and Future

Record: VT-12-024
Title: STT-MRAM: Past, Present, and Future
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 4/11/2014
Time: 10:00 AM
Room Location: CMRR Auditorium
Abstract: It has been 15 years since the first magnetic bits were switched in pillar devices using the spin transfer effect. In November 2012, Everspin announced the first customer sample shipments of STT-MRAM chips. In this talk, I will describe the advances that occurred in the intervening years that have enabled the successful commercialization of STTMRAM technology. I will also describe the challenges that must be overcome to continue scaling this memory to smaller dimensions and consider the potential markets such scaling would open up to this technology. I will conclude with a description of preliminary work being done on electric-field-controlled switching of magnetic bits. Although this research is in its early stages, it offers the potential for switching energies competitive with CMOS transistors, which could enable a new generation of non-volatile logic circuits.

Opportunities and Challenges in Two Dimensional Magnetic Recording

Record: VT-12-023
Title: Opportunities and Challenges in Two Dimensional Magnetic Recording
Authors: Jonathan Coker
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 2/7/2014
Time: 12:00 PM
Room Location: CMRR Auditorium
Abstract: Because conventional perpendicular recording is now reaching its useful limits, the hard drive industry is heavily invested in several alternative recording technologies. The majority of these configurations (such as heat-assisted magnetic recording, microwave-assisted magnetic recording, and bit-patterned magnetic recording) secure their advantages by solving essential problems in the writing process. In contrast, two-dimensional magnetic recording (TDMR) expends its essential focus on the reading process, by providing multiple looks at adjacent written information via multiple read sensors on one slider. This “sleeper” technology was rather abruptly recognized, at a recent conference of recording technologists, as a leading contender for the next generation of HDD technology. While generally thought of as a more conventional option than the alternatives, TDMR nevertheless has profound impact on magnetic component design and on elements of the entire supporting recording system. These impacts will be reviewed in detail from both a magnetic system and a signal-processing perspective. Innovations in linear and nonlinear system identification techniques in two dimensions will be proposed and illustrated.

Meshless Method Solver for Inhomogeneous Electromagnetic Problems and Its application to Microwave Imaging

Record: VT-12-022
Title: Meshless Method Solver for Inhomogeneous Electromagnetic Problems and Its application to Microwave Imaging
Authors: J.A. Katine, Meisong Tong
Group: Patterned Media (Lomakin)
Affiliation: Tongji University, Shanghai, China
Date: 2/7/2014
Time: 2:00 PM
Room Location: CMRR Auditorium
Abstract: Electromagnetic (EM) Problems can be formulated by the integral equations derived from Maxwell’s equations and volume integral equations (VIEs) are indispensable for describing inhomogeneous or anisotropic structures. The solution of VIEs strongly relies on the appropriate discretization of volume integral domains and the meshing work could be very difficult in practice if no special commercial software is used. To reduce the cost of descretizing volume domains, especially remove the constraint of mesh conformity required by the traditional method of moments (MoM), we propose a novel meshless method for solving the VIEs recently. The method is based on the transformation of volume integrals into boundary or surface integrals through the Green–Gauss theorem when integral kernels are regularized by excluding a small cylinder or cube enclosing an observation node. The original integral domain represented by the object is also expanded to a cylindrical or cubic domain enclosing the object to facilitate the evaluation of boundary integrals. The singular integrals over the small cylinder or cube are specially handled with our singularity treatment techniques. The numerical examples for solving inhomogeneous problems with an application to microwave imaging are presented to illustrate the method and good results can be observed.

2013

Magneto-Optic Analysis of Magnetic Microstructures

Record: VT-12-021
Title: Magneto-Optic Analysis of Magnetic Microstructures
Authors: Rudolf Schaefer
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 10/18/2013
Time: 1:00 PM
Room Location: CMRR Auditorium
Abstract: The rich world of magnetic microstructure or magnetic domains, extending from visible dimensions down to the nano-scale, forms the mesoscopic link between the fundamental physical properties of a magnetic material and its macroscopic properties and technical applications, which range from films for computer storage technology to magnetic cores for electrical machinery. Hysteresis phenomena, energy loss in inductive devices, noise in sensors, or the magnetoresistive properties of modern spintronic devices can be decisively determined by the peculiarities of the underlying magnetic microstructure, especially by irreversibilities in the magnetization process. Therefore any development and optimization of magnetic materials, which is usually accompanied by the measurement of magnetization curves, requires an understanding of the underlying domains and their reaction to magnetic fields, which, in most cases, can only be gained by direct imaging. The presentation will address different aspects of magnetic microstructure adapted, where possible, to the interest of the audience and supported by domain observation using Kerr microscopy. This may include domains and magnetization processes in bulk magnetic material like oriented and non-oriented electrical steel, amorphous and nanocrystalline ribbons or permanent magnets, as well as thin films and multilayers. Fast magnetization processes can also be considered. Most challenging is the analysis of hidden (internal) domains and processes in bulk material. They are relevant for material performance and their analysis requires surface imaging in combination with domain modeling and some volume-sensitive imaging method. Aside from their scientific and technical relevance, magnetic microstructures are also aesthetically appealing, an aspect that will be part of the presentation.

Petascale Computational Electromagnetics Methods for Simulating Antennas Near Humans

Record: VT-12-020
Title: Petascale Computational Electromagnetics Methods for Simulating Antennas Near Humans
Authors: Ali Yilmaz
Group: Patterned Media (Lomakin)
Date: 10/18/2013
Time: 11:00 AM
Room Location: CMRR Auditorium
Abstract: The proliferation of wireless communication systems, the appetite for increased functionality of wireless devices, and the lack of conclusive studies on long-term effects of non-ionizing radio-frequency radiation have led to persistent public concern about the possible adverse health effects of radio-frequency power emitting devices in close proximity to humans. While simulation-based bioelectromagnetic (BIOEM) studies have generated an abundance of results inaccessible by experiments in the last three decades, these studies have frequently spawned diverse opinions instead of providing consensus; e.g., on whether the smaller heads of children absorb more radiation and/or allow deeper penetration. Such controversies highlight the pressing need for repr oducible, reliable, high-resolution, and high-accuracy BIOEM simulations—a formidable task because of the complexity of the human body and nearby antennas. This talk will describe our recent progress on developing an integral-equation based simulator that capitalizes on petascale computers to perform unprecedented simulations of antennas near humans. The presentation will describe recently developed FFT acceleration, parallelization, and preconditioning techniques as well as our ongoing validation, verification, and benchmarking efforts. It will also demonstrate the application of the simulator by using the high-fidelity AustinMan and AustinWoman models (AustinMan and AustinWoman are publically available anatomical human models: http://web2.corral.tacc.utexas.edu/AustinManEMVoxels/).

Memristors – Not Just Memory

Record: VT-12-019
Title: Memristors – Not Just Memory
Authors:
Shahar Kvatinsky
Group: Coding & Modulation (Siegel)
Date: 9/30/2013
Time: 3:00 PM
Room Location: CMRR - Auditorium
Abstract: Over the past years, new memory technologies such as RRAM, STT-MRAM, PCM etc., have emerged. These technologies, located in the metal layers of the chip, are relatively fast, dense, and power-efficient and can be considered as memristors. Usually, the use of these devices has been limited to flash, DRAM, and SRAM replacement. This talk is focused on different uses of memristors. For example, memristors can be used as new memory structures, different than the conventional memory hierarchy, opening opportunity to a new era in computer architecture – the era of Memory Intensive Computing. Memristors can also be integrated with CMOS in logic circuits. Alternatively, memristors can be used as a stand-alone logic, suitable to perform logic within the memory and provide opportunity for new computer architectures, different than classical von Neumann.

Advanced spintronic materials for generation and control of spin current

Record: VT-12-018
Title: Advanced spintronic materials for generation and control of spin current
Authors:
Koki Takanashi
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 9/18/2013
Time: 4:00 PM
Room Location: Auditorium
Abstract: “Spin current”, i.e., the flow of spin angular momentum, in magnetic nanostructures has emerged as a fascinating physical concept during the recent development of spintronics. In magnetic nanostructures, magnetism correlates strongly with electronic transport and also other physical properties, leading to the mutual control of magnetic, transport, and other physical properties. Spin current is the most basic concept relevant to the mutual control, and efficient generation and precise control of spin current in magnetic nanostructures are key technologies for the further development of spintronics [1]. There are two kinds of spin current: one is accompanied by an electric current, and the other is not. Spin current without an electric current is called pure spin current, which is actually generated by several experimental methods such as non-local spin injection, spin Hall effect, spin pumping, spin Seebeck effect, and so on. For recent years spin current has been extensively investigated, and particularly the understanding of pure spin current has dramatically developed. In this lecture the concept, historical background, and recent progress in research of spin current will be reviewed, and then some topics on advanced materials for the generation and control of spin current will be introduced, with a focus on magnetic ordered alloys: half-metallic Heusler alloys as a highly efficient spin injector/detector and L10-ordered alloys with high magnetic anisotropy as a perpendicularly polarized spin injector/detector. [1] K. Takanashi, Jpn. J. Appl. Phys., 49 (2010) 110001.

Coding and Signal Processing for Tera-bits-per-square-inch Magnetic Recording

Record: VT-12-017
Title: Coding and Signal Processing for Tera-bits-per-square-inch Magnetic Recording
Authors:
Guan Yong Liang
Group: Coding & Modulation (Siegel)
Date: 7/17/2013
Time: 3:00 PM
Room Location: CMRR Auditorium
Abstract: The Shingled-Write/Two-Dimensional, Heat/Microwave Assisted, and Bit Patterned magnetic recording technologies promise to enable Tera-bits-per-square-inch recording density in future hard disk. However, they are confronted with very challenging channel impairment effects such as 2-dimensional inter-symbol interferences, 2-dimensional colored jitter noise, and unpredictable insertion/deletion errors, as well as prohibitive computational costs. In this talk, the following coding and signal processing techniques developed to address some of these challenges will be presented. Their design methodologies and performance evaluation will be discussed. 1) Reduced-Complexity Iterative Row-Column BCJR Detector for 2-D ISI Channel: This 2-D channel detector essentially reduces the component row or column detector in the well-known IRCSDFA detector from a 2-D BCJR to a 1-D BCJR. Careful iteration scheduling design between the detector and decoder further maintains performance. 2) Dirty-Paper LDPC Code optimized for 2-D ISI Channel: Instead of using a AWGN-optimized LDPC code on a 2-D ISI channel and trying very hard to equalize the severe ISI, we design dirty-paper LDPC codes directly optimized for the "2-D ISI + 2-D detector" super-channel. Dirty-paper code design in this case is possible because the magnetic channel matrix is fairly deterministic per disk. 3) Embedded Marker Code Scheme (EMCS) for Insertion/Deletion Error Channel: The proposed EMCS makes intelligent use of the marker/pinning bits to perform the dual functions of re-synchronization and strengthening the outer LDPC code. Soft synchronization, instead of hard synchronization, further improves performance. 4) 2-D Coding for Multi-Track Reading: When the recording density increases beyond a certain limit, writing and reading multiple tracks may make more sense as the adjacent-track interference can now be "absorbed" into the symbols written on multiple tracks. In 3x3 ISI channels, we found that it works very well to encode using non-binary LDPC over GF(4), write every code symbol on two tracks, detect 3 tracks, and perform joint detection decoding over 4 tracks.

Reproducible Equalization and detection for two-dimensional intersymbol-interference channels

Record: VT-12-016
Title: Reproducible Equalization and detection for two-dimensional intersymbol-interference channels
Authors: Shayan Srinivasa
Group: Coding & Modulation (Siegel)
Date: 5/8/2013
Time: 2:00 PM
Room Location: Auditorium
Abstract: Two-dimensional (2-D) intersymbol-interference (ISI) channels have become practically relevant in various data recording technologies, such as, two-dimensional magnetic recording (TDMR), bit patterned media (BPM), optical holographic memories, as well as in wireless channels and 2-D grid networks. We first present a 2-D detection method by extending the 1-D maximum a-posteriori (MAP) detection algorithm to operate over multiple rows and columns, in an iterative manner, by using feedback information from adjacent rows/columns. We study the performance vs. complexity trade-offs for various trellis configurations. A novel self-iterating 2-D linear minimum mean-squared error based equalizer is developed by extending the 1-D linear equalizer. The 2-D self-iterative equalizer and detection engines exchange soft-information within a turbo-equalization set up. The performance is near MAP with tractable complexity, and beats the Marrow-Wolf detector by about 0.6 dB. The coded performance with the 2-D equalizer-detector engine indicates about 8 dB of SNR gain over the un-coded system.

Magnetization Dynamics Critical Curves of Coupled Magnetic Systems

Record: VT-12-015
Title: Magnetization Dynamics Critical Curves of Coupled Magnetic Systems
Authors: Leonard Spinu
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 4/12/2013
Time: 11:30 AM
Room Location: Auditorium
Abstract: Magnetization dynamics in nanosized magnetic objects is of great importance both for fundamental studies and technological applications. Magnetic nanowires are considered one of the best candidates to be used in specialized devices for modern communications and as recording elements in future ultra-high density media. If present fabrication techniques can produce magnetic nanowires arrays with a very well controlled morphology there are still numerous problems in understanding their properties. In this talk we will present our results in probing the dynamics of two-dimensional N80Fe20 nanowire arrays with different strength of interwire interactions using angular dependent microwave absorption spectroscopy. The experimental results are analyzed in terms of a new graphical representation of the resonant absorption data through a critical-curve-like approach. This new representation has the advantage of offering a direct and complete visual representation of anisotropy, interactions and magnetization dynamics effects in nanomagnet arrays. The proposed image of polar resonant absorption curves offers the benefit of a pictorial fingerprinting-like method, while being complete and accurate, which is useful for a rapid differentiation of samples of different morphologies and/or subject to different microwave irradiations. In this talk we will reveal the connection between this new representation and the static switching field critical curves.

Spinterfaces as microscopic spin traps

Record: VT-12-014
Title: Spinterfaces as microscopic spin traps
Authors: Mirko Cinchetti
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 4/9/2013
Time: 3:30 PM
Room Location: Auditorium
Abstract: Interfaces between ferromagnetic materials and organic semiconductors – also known as spinterfaces - constitute an incredibly rich playground in the field of spintronics. For example, spinterfaces have the potential to be implemented as tunable spin filters, which will pave the way to a whole new class of advanced, i.e., actively controlled spintronics devices. The progress in the field of spinterface science depends thus critically on elucidating the still unexplored spin-dependent carrier dynamics at such hybrid interfaces. We use time-resolved two-photon photoemission to optically pump and probe a hybrid electronic state forming at the prototypical spinterface between cobalt and the organometallic complex tris(8-hydroxyquinolinato)aluminium (Alq3). We generate a transient spin polarization in the hybrid interface state, and follow its behavior in four dimensions: energy, time, spin and momentum. We find that electrons are confined at the Co-Alq3 interface for times in the range of 0.5-1 ps, and that the confining potential is strongly spin dependent. Such spin-dependent trapping behavior elucidates the fundamental microscopic origin of the spin-filtering properties at spinterfaces, which is important for the design of next-generation spintronics devices based on tunable organic spin filters.

Ab-initio calculations of the lattice thermal conductivity from an exact solution of the Boltzmann-Peierls equation

Record: VT-12-013
Title: Ab-initio calculations of the lattice thermal conductivity from an exact solution of the Boltzmann-Peierls equation
Authors: Laurent Chaput
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 3/13/2013
Time: 1:30 PM
Room Location: Auditorium
Abstract: In this work we present ab-initio calculations of the lattice thermal conductivity and related quantities for several semiconductors of interest in energy transport and thermoelectricity. Excellent agreements with experiments are obtained. A new method is proposed to obtain a numerically exact and fast solution to the Boltzmann-Peierls equation. This is made possible using the symmetries of the systems and open the way to the theoretical design of new materials. The collision kernel of the equation is constructed using an efficient parallelization of the code over the irreducible triplets of phonon wavevectors involved in the different possible collisions. These irreducible triplets are the equivalent of the irreducible part of the Brillouin zone for single particle quantities. Therefore a formulation of the self energy and collision kernel based on their use drastically reduce the computational time.

NANOCOMPOSITE MAGNETS FOR POWER ELECTRONIC APPLICATIONS

Record: VT-12-012
Title: NANOCOMPOSITE MAGNETS FOR POWER ELECTRONIC APPLICATIONS
Authors: Michael McHenry
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 3/12/2013
Time: 3:30 PM
Room Location: Auditorium
Abstract: Recent USDOE workshops highlight the need for advanced soft magnetic materials leveraged in novel designs of power electronic components and systems for power conditioning and grid integration. Similarly soft magnetic materials figure prominently in applications in electric vehicles and high torque motors. Dramatic weight and size reductions are possible in such applications. Nanocomposites also hold potential for applications in active magneocaloric cooling of such devices. Bulk and thin film soft magnet sensors can contribute to the search for oil and critical materials. Opportunities for state of the art soft magnetic materials to impact such applications have been helped by investment by USDOD Programs and other world wide efforts to advance these materials for applications in military electric vehicle technologies. This talk will focus on the framework for developing high frequency (f) magnetic materials for grid integration of renewable energy sources bridging the gap between materials development, component design, and system analysis. Examples from recent efforts to develop magnetic technology for lightweight, solid-state, medium voltage (>13 kV) energy conversion for MW-scale power applications will be illustrated. The potential for materials in other energy applications (motors, cooling, sensors, RF metal joining, etc.) will also be discussed. The scientific framework for nanocomposite magnetic materials that make high frequency components possible will be presented in terms of the materials paradigm of synthesis ? structure ? properties ? performance. In particular, novel processing and the control of phase transformations and ultimately nanostructures has relied on the ability to probe structures on a nanoscale. Examples of nanostructural control of soft magnetic properties will be illustrated.

Robotic Surgery-From Application Specific Robots to Single-Use Robots

Record: VT-12-011
Title: Robotic Surgery-From Application Specific Robots to Single-Use Robots
Authors: Tim Lueth
Group: Tribology & Mechanics (Talke)
Date: 3/12/2013
Time: 4:00 PM
Room Location: CMRR Conference Room
Abstract: Since 2005, robots in medical procedures have become extremely helpful tools in surgery, radiation therapy, and imaging. In this talk, the development of different types of surgical robotics systems is described. The basic principles of these systems, and the procedures and approvals needed before their use in surgery are discussed. A new concept of single use robotic systems is presented using the example of a snake-like robot for minimally invasive surgery. This type of robot can be designed semi-automatically and can be custom manufactured in less than 24 hours using selective laser sintering.

Tunnel –mediated coupling between antiferromagnetic thin films

Record: VT-12-010
Title: Tunnel –mediated coupling between antiferromagnetic thin films
Authors: Alexandre Bataille
Group: Magnetic Films and Nanostructures (Fullerton)
Date: 2/13/2013
Time: 3:30 PM
Room Location: Auditorium
Abstract: The study, tailoring and control of the coupling between magnetic layers triggered the development of spintronics, notably by leading to the discovery of giant magnetoresistance, and by allowing the tuning of the coercivity and exchange field of ferromagnetic thin films through exchange bias. Up to now, only systems comprising at least one ferromagnetic film exhibit some magnetic coupling. Here we present a system where two antiferromagnetic layers separated by an ultrathin tunnel barrier interact with each other. We have chosen to study Cr/MgO/Cr trilayers since chromium is a model antiferromagnet [1], and has a band structure rather similar to other bcc metals like Fe. Bulk Cr exhibits an incommensurate spin density wave (SDW) structure below TN=311K, coupled with a charge density wave (CDW). We have grown a series of epitaxial Cr/MgO/Cr trilayers, in which the MgO thickness varies between 3 and 11ML. We have determined the magnetic state of our trilayer samples by combining neutron diffraction measurements (to determine the polarization of the SDW and detect the presence of commensurate phases) and high resolution X-ray diffraction studies (to measure the CDW/SDW period(s) and locate the corresponding phases in the top or bottom layer, which lattice parameters differs slightly). Our results show that the magnetic state of the trilayers cannot be deduced from the properties of the individual Cr layers (supplementary phases appear, with altered periods) for MgO thicknesses below a critical value of 4ML. We attribute [2] this behavior to a tunnel mediated coupling between the Cr layers, in analogy to what has been observed for the Fe/MgO/Fe system. This interpretation is supported by our recent angle-resolved photoemission measurements, which evidence the presence of a resonant state at the Cr/MgO interface, leading to a significant overlap of the wavefunctions linked to Cr magnetism across the MgO barrier. 1.E. Fawcett, Rev. Mod. Phy.s 60 209 (1988) 2.M.-A. Leroy et al., submitted to Nature Communications

Polar Codes for Data Storage

Record: VT-12-009
Title: Polar Codes for Data Storage
Authors: Warren Gross
Group: Coding & Modulation (Siegel)
Date: 2/1/2013
Time: 1:30 PM
Room Location: CMRR - Auditorium
Abstract: Polar codes are a new class of error-correcting codes that provably achieve the capacity of memoryless channels with low complexity encoding and decoding algorithms. In this work, we survey the literature and investigate the suitability of polar codes to data storage applications focusing on error-correction performance and throughput. We show that polar codes meet the criteria for such applications and highlight the work required before practical data storage systems can utilize these codes.

Half-Metallicity and Ultrafast Magnetization Dynamics in Heusler Compounds

Record: VT-12-008
Title: Half-Metallicity and Ultrafast Magnetization Dynamics in Heusler Compounds
Authors: Daniel Steil
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: University of Kaiserslautern
Date: 1/29/2013
Time: 3:30 PM
Room Location: CMRR - Auditorium
Abstract: Several intermetallic Heusler compounds are predicted to be half-metallic ferromagnets (FM), meaning that a band gap exists at the Fermi level in one of the spin channels. This property makes them highly interesting sources of spin-polarized currents and attractive materials for all kinds of spintronics devices, like the well-known magnetoresistive hard disc read heads. Unfortunately, a direct proof of half-metallicity is problematic at best. Most methods to probe the spin-polarization of a material are surface- (e.g., spin-polarized photoemission) or interface-sensitive (e.g., tunneling magnetoresistance). Effects, like symmetry-breaking at surfaces, can alter the measured surface spin-polarized density of states (DOS) compared to the bulk DOS. To overcome this challenge, bulk-sensitive time-resolved Kerr magnetometry (TR-MOKE) was suggested as a probe for half-metallicity, as a minority band gap should slow down magnetization dynamics compared to the 3d-FM [1]. However, Heusler compounds typically show magnetization dynamics similar to the 3d-FM [1-3], which has been partly attributed to defect states destroying the half-metallicity [1]. In my talk I will discuss selected results of studies on the Heusler compounds Co2MnSi (CMS) and Co2FeSi (CFS) concerning their possible half-metallicity and the applicability of TR-MOKE to probe a half-metallic DOS. Furthermore. I will give an outlook on the Half-Heusler system NiMnSb, which shows a rich variety of ultrafast magnetization dynamics. [1] G.M. Müller et al.; NMat 8, 56 (2009) [2] D. Steil et al., PRL 105, 217202 (2010) [3] J.-P. Wüstenberg et al., PSS B 248, 2330 (2011)

2012

CALCULATION OF SUB-LATTICE MAGNETIZATION OF BARIUM FERRITE PERMANENT MAGNET FOR (BH)MAX PREDICTION

Record: VT-12-007
Title: CALCULATION OF SUB-LATTICE MAGNETIZATION OF BARIUM FERRITE PERMANENT MAGNET FOR (BH)MAX PREDICTION
Authors: Yang-Ki Hong
Group: Magnetic Materials & Devices (Berkowitz)
Affiliation: University of Alabama
Date: 12/14/2012
Time: 1:30 PM
Room Location: Center for Magnetic Recording Research Auditorium
Abstract: Five distinct magnetic sites exist in barium ferrite. We have described the calculation of five sub- lattice magnetizations for barium ferrite permanent magnet to predict elevated temperature maximum energy product (BH)max. The first-principles calculations, based on density functional theory, were performed to calculate magnetic moment at 0K and the Neel temperature for each site. Then, the moment and the Neel temperature were used to fit with the Brillouin function to construct temperature dependence of magnetization, thereby predicting (BH)max.

Reproducible Control of the Magnetic Vortex Chirality on a Nanosecond Timescale

Record: VT-12-006
Title: Reproducible Control of the Magnetic Vortex Chirality on a Nanosecond Timescale
Authors: Vojtech Uhlir
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: UCSD
Date: 12/4/2012
Time: 4:00 PM
Room Location: Center for Magnetic Recording Research Auditorium
Abstract: Magnetic vortices are curling magnetization structures which represent the lowest energy state in sub-micron size magnetic disks or polygons. The vortex core, a singularity at the vortex center, features magnetization pointing either up or down perpendicular to the disk plane. The binary character of the chirality of the curl and the polarity of the vortex core leads to four possible stable magnetization configurations that can be utilized in a multi-bit memory cell. Both the vortex polarity and chirality are stable against static magnetic fields. It has been shown that when excited with ultrafast magnetic field or current stimuli, the core polarity can be reversed on a 100 ps timescale.

New Coding Methods for Nonvolatile Memories

Record: VT-12-005
Title: New Coding Methods for Nonvolatile Memories
Authors: Anxiao (Andrew) Jiang
Group: Non-volatile, Solid-State Memory (Swanson)
Affiliation: Texas A&M University
Date: 11/27/2012
Time: 4:00 PM
Room Location: Center for Magnetic Recording Research Auditorium
Abstract: Coding for nonvolatile memories will be an important development in data storage technologies. Currently, there has been lots of interest in coding for flash memories, and many results have been derived. In this talk, I will discuss new topics in coding theory for data storage in flash memories and related nonvolatile memories. Like magnetic recording and optical recording, flash memories have their own distinct properties, including recursive programming, block erasure, etc. These distinct properties introduce very interesting coding problems that address many aspects of a successful storage system, which include efficient data modification, error correction, high density storage, and more. I will introduce the challenges of flash memories and related nonvolatile memories, review the existing coding techniques, -- including codes for rewriting data, rank modulation, error correction, and variable-level cell -- and look forward to some potential approaches for the future.

Spin caloritronics – more than spin-dependent thermoelectrics

Record: VT
Title: Spin caloritronics – more than spin-dependent thermoelectrics [IEEE]
Authors: Gerrit Bauer
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: Institute of Materials Research, Tohoku University, Japan and Kavli Institute of NanoScience, TU Delft, The Netherlands
Date: 11/13/2012
Time: 4:00 PM
Room Location: CMRR Auditorium
Abstract: The spin degree of freedom of the electron affects not only charge, but also heat and thermoelectric transport, leading to new effects in small structures that are studied in the field of spin caloritronics (from calor, the Latin word for heat). This lecture addresses the basic physics of spin caloritronics. Starting with an introduction into thermoelectrics and Onsager’s reciprocity relations, the generalization to include the spin dependence in the presence of metallic ferromagnets will be addressed. Using this foundation I will describe several recently discovered spin-dependent effects in metallic nanostructures and tunneling junctions in terms of a two spin-current model of non-interacting. Next, I will argue that a different class of spin caloritronic effects exists that can be explained only by the collective spin dynamics in ferromagnets. The thermal spin transfer torque that allows excitation and switching of the magnetization in spin valves as well as the operation of nanoscale heat engines is complemented by thermal spin pumping. The latter generates the so-called spin Seebeck effect, which is generated by a heat current-induced non-equilibrium of magnons at a contact between an insulating or conducting ferromagnet and a normal metal. Under these conditions a net spin current is injected or extracted from the normal metal that can be detected by the inverse spin Hall effect. Both classes of effects can be understood in the adiabatic approximation for the magnetization dynamics and computed in terms of material-dependent electronic structures. Further issues to be addressed are the relation between electric, thermal and acoustic actuation of the magnetic order parameter, as well as the application potential of spin caloritronics.

Recent trends in understanding of spintronic phenomena in magnetic tunnel junctions and graphene based structures

Record: VT
Title: Recent trends in understanding of spintronic phenomena in magnetic tunnel junctions and graphene based structures
Group: Patterned Media (Lomakin)
Affiliation: SPINTEC, CEA/CNRS/UJF-Grenoble/G-INP, INAC, Grenoble, France
Date: 8/14/2012
Time: 4:00 PM
Room Location: CMRR Auditorium
Abstract: The discoveries of giant magnetoresistance(GMR) [1] in magnetic multilayers and of tunnel magnetoresistance [2] (TMR) in magnetic tunnel junctions (MTJ) generated a new field of research called spin electronics3 (spintronics) [3]. In this field, it is not only the electron charge but also the electron spin that is used to operate a device. This seminar will be devoted to an overview of spintronic phenomena in magnetic nanostructures with particular attention paid to demonstrating how theory helps advancing device applications. I will start from recent progress in theory of spin transfer torques (STT) in MTJs which in particular allowed prediction of STT voltage dependences and provided solutions for STT-MRAM [4,5]. Next part of the talk will be devoted to studies of interlayer exchange coupling (IEC) using ab-initio and tight-binding approaches. In particular, we will address the impact of structural relaxation and interfacial oxidation conditions on amplitude of IEC in MTJs [6] as well as the importance of occupation numbers (Fermi level) on period of IEC oscillations as a function of ferromagnetic electrode thickness [7] and dynamics of exchange coupled magnetic moments [8]. I will continue with ab-initio investigations of perpendicular magnetic anisotropy (PMA) at Fe(001)|MgO(001) and Co(001)|MgO(001) interfaces along with identifying mechanisms responsible for the PMA [9]. It will be demonstrated that the oxidation conditions strongly affect the PMA and it strongly correlates with tunnel magnetoresistance (TMR) in agreement with experiments [9,10]. The seminar will be concluded by first-principles investigations of magnetic properties of graphene-based structures in a view of graphene spintronics including Co|graphene interfaces [11] and substrate and shape induced magnetism in graphene [12]. -- [1] M. Baibich, J. M. Broto, A. Fert et al, Phys. Rev. Lett. 61, 2472 (1988); G. Binasch, P. Grunberg, F. Saurenbach, W. Zinn, Phys. Rev. B 39, 4828 (1989). [2] J. S. Moodera et al, Phys. Rev. Lett. 74, 3273 (1995) ; T. Miazaki et al, JMMM, 139, L231 (1995). [3] A. Fert et al, Mat. Sci. Eng. B, 84, 1 (2001) ; S. A. Wolf, Science, 294, 1488 (2001). [4] I. Theodonis et al, Phys. Rev. Lett. 97, 237205 (2006); M. Chshiev et al. IEEE Trans. Mag. 44 (11) (2008); A. Manchon et al, J. Phys. Cond. Mat. 20, 145208 (2008); A. Kalitsov et al, Phys. Rev. B 79, 174416 (2009). [5] S.-C. Oh et al, Nature Physics 5, 898 (2009). [6] H. X. Yang et al, Appl. Phys. Lett. 96, 262509 (2010). [7] L. E. Nistor et al, Phys. Rev. B 81, 220407 (2010). [8] D. Terrade et al, in preparation. [9] H. X. Yang et al, Phys. Rev. B 84, 054401 (2011). [10] L. E. Nistor et al, IEEE Trans. Magn. 46, 1412 (2010). [11] Chi Vo-Van et al, New J. Phys. 12, 103040 (2010); J. Coraux et al, J. Phys. Chem. Lett. 3, 2059 (2012). [12] H. X. Yang et al, Phys. Rev. B 84, 214404 (2011).

Challenges in Electromagnetic Modeling of Large Multiscale Systems

Record: VT-12-004
Title: Challenges in Electromagnetic Modeling of Large Multiscale Systems
Group: Patterned Media (Lomakin)
Affiliation: Michigan State University
Date: 5/15/2012
Time: 4:00 PM
Room Location: CMRR Auditorium
Abstract: Understanding electromagnetic field distributions plays a key role in a range of devices; from photonic circuits to packaging to metamaterials to antennas to EMC/EMI issues, etc. While this list is long, the ability to simulate electromagnetic fields in realistic devices requires the discretization to span multiple scales; from 10−5λ ≤ h ≤ 0.1λ. Such wide variation in mesh density implies that any methodology should (i) be mesh-robust, highly adaptable and well conditioned, and (ii) be integrated with a methodology whose computational cost and memory complexity scale almost linearly with the number of the unknowns. This talk will present some of our work to date on addressing these two problems. The approach that we have espoused to tackling the first relies on a variant of the method of moments. Since their inception, most surface integral equation solvers have relied on a simplicial, piecewise smooth tessellation of the scatterer surface. This representation of the object and the approximation spaces that are defined on it are highly restrictive in terms of accuracy and refinement. We will present recent work based on a highly flexible surface approximation scheme that can start from an arbitrary description of the underlying scatterer. Starting from these surface parameterization we will design a framework to construct basis functions, providing for near-complete freedom in choice of the approximation space. We will show that this can lead to the development of a solution scheme for surface integral equations that permit multiple classes of geometry descriptions, multiple types of basis functions and easy h−,p−, and hp− adaptivity in both surface and function approximation. Next, it is well known that objects will dense discretization, significantly more than what is necessary to capture phase variation, pose a bottleneck to the use of acceleration techniques. The problem can be rephrased as those occurring at transition points in the electromagnetic spectrum, from RF to DC and RF to optics. This talk will focus on both recent and no-so recent efforts to bridge these transitions. Examples illustrating the efficacy of these methods and their application to a range of problems will be presented.

Science and Technology of Modern Permanent Magnet Materials

Record: VT-12-003
Title: Science and Technology of Modern Permanent Magnet Materials
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: University of Delaware
Date: 4/5/2012
Time: 2:00 PM
Room Location: CMRR Auditorium
Abstract: Permanent magnets (PMs) are indispensable for the electric, electronic and automobile industries, information technologies, automatic control engineering and many other commercial and military applications. In most of these applications, an increase in the magnetic energy density of the PM, usually presented via the maximum energy product (BH)max, immediately increases the efficiency of the whole device and makes it smaller and lighter. Worldwide demand for high performance PMs has increased substantially in the past few years driven by hybrid and electric cars, wind turbines and other power generation systems. A dramatic improvement in the performance of PMs was made during the 20th century, with (BH)max increased by more than 100 times, as a result of major advances in solid state physics, materials science and metallurgy. However, new energy challenges in the world require devices with higher energy efficiency and minimum environmental impact. The potential of 3d-4f compounds that revolutionized PM science and technology is nearly fully utilized, and the supply of 4f rare earth elements is no longer assured. This lecture will cover the major principles guiding the development of PMs, including the important role of microstructure on coercivity, and overview state-of-the-art theoretical and experimental research. Recent progress in the development of nanocomposite PMs, consisting of a fine (at the scale of magnetic exchange length) mixture of phases with high magnetization and large magnetic hardness will be discussed. Fabrication of such PMs is currently the most promising way to boost the (BH)max, while simultaneously decreasing, at least partially, the reliance on the rare earth elements. Current efforts in the development of high performance non-rare earth magnets and their future prospects will also be discussed.

Soft Magnetic Thin Film Applications at Radio Frequencies

Record: VT-12-002
Title: Soft Magnetic Thin Film Applications at Radio Frequencies
Authors:
Masahiro Yamaguchi
Group: Magnetic Films and Nanostructures (Fullerton)
Affiliation: Tohoku University
Date: 2/21/2012
Time: 4:00 PM
Room Location: CMRR Auditorium
Abstract: Development of new passive component technologies will enable a “More-than-Moore” paradigm leading to innovative application-specific compact systems [1]. Ferromagnetic thin film materials, having high permeability at (and above) radio frequencies, are candidate materials for use in inductive passive components that are available in the forms of vacuum-deposited and electro-deposited metallic alloys, chemically synthesized nano-particulate composites, and traditional oxides, among others. Using these materials, the development of CMOS integrated inductors and integrated electromagnetic noise suppressors for Long Term Evolution, or 3.9th Generation, cell phone RFIC and Point-of-Load one-chip DC-DC converters, is attracting great interest from both academic and industrial communities. This lecture begins with a review of new soft magnetic thin film applications at radio frequencies for future system-in-package (SiP) and system-on-chip (SoC) technologies. Proposed in late 1970s, these thin film soft magnet applications have evolved from inductive read/write recording head technology to the frontiers of GHz frequency device applications. Discussions covered in this lecture include: (1) Development of international cross measurements of RF permeameters [2] to evaluate RF permeability and related FMR profiles of magnetic films; (2) small signal high permeable low loss applications to CMOS integrated inductors [3]; (3) small signal lossy application to CMOS integrated electromagnetic noise suppressor [4]; (4) small to medium signal applications as new metal/ferromagnetic multi-stack “conductors” to suppress skin effect utilizing negative permeability beyond the FMR frequency [μr’< 0, μr”≈0][5]; and, (5) large current permeable application to Point-of-Load type one-chip DC-DC converters. The lecture will conclude with an outlook that provides a perspective on the future of on-chip RF magnetics. 1] John P. Kent, and Jagdish Prasad, “Microelectronics for the Real World: ‘Moore’ versus ‘More than Moore’,” IEEE 2008 Custom Integrated Circuits Conference, 15-4-1 (2008). [2] M. Yamaguchi, Y. Miyazawa, K. Kaminishi and K.I. Arai, “A New 1 MHz-9 GHz Thin-Film Permeameter Using a Side-Open TEM Cell and a Planar Shielded-Loop Coil,” Trans. Magnetic Society of Japan, 3, 137-140 (2003). [3] Masahiro Yamaguchi, Keiju Yamada, Ki Hyeon Kim, "Slit Design Consideration on the Ferromagnetic RF Integrated Inductor," IEEE Transactions on Magnetics, 42, 3341-3343 (2006) [4] Sho Muroga, Yasushi Endo, Wataru Kodate, Yoshiaki Sasaki, Kumpei Yoshikawa, Yuta Sasaki, Makoto Nagata Masahiro Yamaguchi, “Evaluation of Thin Film Noise Suppressor Applied to Noise Emulator Chip Implemented in 65nm CMOS technology,” IEEE Transaction on Magnetics, 48, 4485 - 4488 (2011). [5] Masahiro Yamaguchi, Yutaka Shimada, Takayoshi Inagaki and Behzad Rejaei, “Skin Effect Suppression in RF Devices Using a Multilayer of Conductor and Ferromagnetic Thin Film with Negative Permeability,” Microwave Workshop and Exhibition 2008 (MWE 2008), WS08-03 (Yokohama, 2008).

Mechanism of Magnetic Anisotropy and Its Temperature Dependence: Alternative Recording and Permanent Magnet Materials

Record: VT-12-001
Title: Mechanism of Magnetic Anisotropy and Its Temperature Dependence: Alternative Recording and Permanent Magnet Materials
Group: General
Affiliation: Lomakin
Date: 2/14/2012
Time: 4:00 PM
Room Location: CMRR Auditorium
Abstract: Magnetic recording technology and permanent magnet applications demand alternative magnetic materials with improved magnetic anisotropy energy (MAE) and its temperature dependence. Rapidly decreasing grain size of data storage media requires large anisotropy within the corrosion resistive material set with suitable temperature dependence. Permanent magnet for electric vehicle (EV) and wind turbine applications are facing severe challenges due to limited availability, pricing and environmental hazard of mining rare-earth materials (RE). In this presentation I focus on mechanisms of MAE and its temperature dependence for two classes of materials (i) M-X where M=( Fe, Co), X= (Pt, Pd) and (ii) Mn-Y where Y=(Al, Bi). To gain necessary understanding of MAE and its temperature dependence we employ multi-scale modeling approach which combines a microscopic model of the magnetic interactions and statistical modeling/theory techniques [1,2]. The microscopic model of the magnetic interactions is tested against measurements of the temperature dependent magnetic properties for nano-particulate and granular FePt thin films [3] including MnBi with anomalous dependencies [4]. I conclude with summary of examples for calculations of complete set of material parameters (Tc,A, Ms, K) needed to guide search/development of alternative materials for discussed applications. References: [1]. O. N. Mryasov , U. Nowak, K. Guslienko, R.W. Chantrell EuroPhysics Letters, 69(5), 805 (2005). [2]. O.N. Mryasov, Journal of Magnetism and Magnetic Materials, v. 272-276, p.800, (2004). O.N. Mryasov et al., JPCM 3, 7683-7690 (1991); O.N. Mryasov, et al., PRB 45, 12330 (1992). [3]. S. Okamoto et al. Phys. Rev. B, 66, 024413 (2002); J. U. Thiele et al., J. Appl. Phys. 91, 6595 (2002). [4]. X.Guo et al., Phys. Rev. B. 46, 1478 (1992).