Seminars and Presentations
| Date | Seminar | Presenter | Abstract |
|---|---|---|---|
| October 5, 2018 | Iron Garnets: Enabling Materials for Magnonics, Photonics, and Spintronics | Professor Caroline Ross - Associate Head of the Department of Materials Science and Engineering, Massachusetts Institute of Technology | Ferromagnetic insulator thin films have emerged as an important component of magnonic, spintronic and magnetooptical devices. Yttrium iron garnet in particular is an excellent insulator with low Gilbert damping and a Néel temperature well above room temperature, and has been incorporated into heterostructures that exhibit a plethora of spintronic and magnonic phenomena including spin pumping, spin Seebeck, proximity effects and spin wave propagation. Epitaxial rare earth (RE) garnet films are both magnetic and magnetoelastic, and their properties can be manipulated by choice of composition and substrate lattice mismatch, including making films with perpendicular magnetic anisotropy (PMA) and obtaining a room temperature compensation temperature. We demonstrate robust PMA in films of thulium, europium and terbium iron garnet (TmIG, EuIG and TbIG) with high structural quality down to a thickness of 5.6 nm, about 5 unit cells. RE garnet/Pt bilayers exhibit efficient spin transmission across the garnet/Pt interface, and we achieved bidirectional switching of the magnetization of TmIG at room temperature via domain wall translation at velocities exceeding 800 m/s, faster than all-metal systems. RE garnet/Pt bilayers exhibit a Dzyaloshinskii-Moriya interaction and 10 nm magnetic domain sizes making them suitable systems for skyrmion generation. Iron garnets also exhibit magnetooptical activity and high transparency in the infrared, which makes them useful non-reciprocal materials at communications wavelengths. We incorporated Ce- and Bi-substituted YIG into integrated magnetooptical isolators to control the flow of light in photonic integrated circuits. |
| May 12, 2017 | Nano-magnetic Manipulation of Cells | Professor Dino Di Carlo, Ph.D. - Professor and Graduate Vice Chair, UCLA Department of Bioengineering | Developing the next generation of tools to automate cell biology research and quantitatively separate the most active cells for cell therapies requires new approaches to interfacing at the cellular and sub-cellular scale. My lab is developing a set of tools to de-amplify macroscale motions and forces to nanoscale perturbations to separate and locally stimulate cells. I will discuss the core of this platform - a micromagnetic substrate composed of: i) electroplated soft magnetic (NixFey) elements, ii) a biocompatible, planarized resin layer, and iii) lithographically patterned micro-magnet arrays. Magnetizing the micro-magnetic elements with a permanent magnet generates large magnetic potential minima that rapidly and precisely apply magnetic forces on nanoparticles attached to the surface of or inside of cells. We have used this platform to perform quantitative equilibrium separations of cells based on surface expression by labeling with superparamagnetic nanoparticles as well as select mutant magnetotactic bacteria that produce increased numbers of magnetic nanoparticles. By applying forces on nanoparticles bound to the surface of cortical neurons we were able to control calcium signaling locally within neural networks and bias the direction of neural network growth. By applying forces approaching the yield tension of single cells, we were also able to generate coordinated responses in cellular behavior, including the PAK-dependent generation of active, leading-edge type filopodia, and significant (45 to 90 degree) biasing of the metaphase plate during cell mitosis. The technique shows promise as a tool for cell purification, analysis and engineered control. |
| March 3, 2017 | Career Development Series Part III: Pitch Perfect Resume Writing | David Blancha, UCLA Career Center, STEM Manager- Graduate Student Services | In this session, we will discuss how to gain small edges in writing professional documents, using the resume as the primary example. By understanding the needs of your reader and the environment your documents will be read in, you can be sure to stand out in positive ways that reinforce your professional identity. |
| February 24, 2017 | Ultrafast and Very Small: Discover Nanoscale Magnetism With Picosecond Time Resolution Using X-Rays | Dr. Hendrik Ohldag, 2017 IEEE Distinguished Lecturer/SLAC | Today’s magnetic device technology is based on complex magnetic alloys or multilayers that are patterned at the nanoscale and operate at gigahertz frequencies. To better understand the behavior of such devices one needs an experimental approach that is capable of detecting magnetization with nanometer and picosecond sensitivity. In addition, since devices contain 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 electron volts up to tens of kiloelectron volts. 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 its orientation or determine the orientation of the spin axis in an antiferromagnet. The wavelength of X-rays is on the order of nanometers, which enables microscopy with nanometer spatial resolution. And finally, a synchrotron is a pulsed X-ray source, with a pulse length of tens of picoseconds, 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 to the field and explain the capabilities of synchrotron based X-ray microscopy, which is becoming a tool available at every synchrotron, to a diverse audience. The general introduction will be followed by a set of examples, depending on the audience, that may include properties of magnetic materials in rocks and meteorites, magnetic inclusions in magnetic oxides, interfacial magnetism in magnetic multilayers, and dynamics of nanostructured devices due to field and current pulses and microwave excitations. |
| February 17, 2017 | Career Development Series Part II: Networking to Create and Manage Your Professional Identity | David Blancha, UCLA Career Center, STEM Manager- Graduate Student Services | In this session, we will discuss and practice the necessary elements of networking at structured networking events, online, and in unstructured social/professional situations. |
| February 10, 2017 | Career Development Series Part I: Developing Your Professional Timeline | David Blancha, UCLA Career Center, STEM Manager- Graduate Student Services | In this session, we will discuss how to assess and evaluate your current position in your professional development, and offer practical strategies to pursue your career goals with careful benchmark setting, skill gap assessment, SMART goal setting, and time management. |
| February 3, 2017 | Energy efficient nanomagnetic computing with electric field control of magnetization | Professor Jayasimha Atulasimha, Virginia Commonwealth University | We have shown that multiferroic nanomagnets (consisting of a piezoelectric and a magnetostrictive layer) can be used to perform computing while dissipating ~ few aJ/bit at clock rates of ~1GHz. This talk will discuss our work on understanding strain triggered magnetization dynamics in the presence of thermal noise in magnetostrictive nanomagnets to implement computing devices that are resilient to thermal noise at room temperature. Demonstration of strain clocked nanomagnetic logic in Co nanomagnets [1] patterned on a PMN-PT substrate and experiments that demonstrate that a surface acoustic wave (SAW) can drive a single domain nanomagnet into a non-volatile vortex state [2] will be presented. A recent research effort in our group: core reversal of fixed magnetic skyrmions with voltage control of magnetic anisotropy (VCMA) without applying a magnetic field [3] will also be discussed. This could lead to the possibility of a new direction for energy efficient nanomagnetic computing implemented with fixed skyrmions without moving them with a current. This talk will conclude with our assessment of future research needed to address some of the key materials and characterization challenges that must be overcome to make these extremely low energy nanomagnetic switching paradigms viable for practical computing devices. Other potential applications of the ability to control nanoscale magnetization with an electric field will also be discussed. |
| December 2, 2016 | Spintronic Materials and Devices for Memory and Logic: Prospects and Challenges for Beyond CMOS Applications | Professor Jian-Ping Wang, University of Minnesota Department of Electrical and Computer Engineering | An energy efficient and high density memory and logic device for the post-CMOS era has been the goal of a variety of industry applications. The limits of scaling, which we expect to reach by the year 2025, demand that future advances in computational power will not be realized from ever shrinking device sizes, but rather by innovative architectures and new materials and physics. Magnetoresistive based devices have been a promising candidate for future integrated magnetic memory and computation because of its unique non-volatility, endurance and other functionalities. The application of perpendicular magnetic anisotropy for potential STT-RAM application was demonstrated and later has been intensively investigated by both academia and industry groups, but there is no clear path way how scaling will eventually work for both memory and logic applications. One of the main reasons is that there was no demonstrated material stack candidate that could lead to a scaling scheme down to sub 10 nm. Another challenge for the usage of magnetoresistive-based devices for memory and logic application is its high operational energy. In this talk, I will review the recent progress we have made to address those two key challenges. Then I discuss the opportunities and some potential path ways for high density and 3D magnetoresistive based devices for memory and logic applications and their integration. By the end, I will introduce several system level applications enabled by spintronic memory and logic, e.g. non-volatile processors for internet of things. I will share a specific example on a new architecture based on 2T-1C MTJ array to allow computation in memory, which we name as computational random access memory (CRAM). |
| November 4, 2016 | Innovative Design and Mechanisms for ASsembling and Manipulation of Nanomotors with Ultrahigh Performances - for Biochemical Removal, Release, and Microfluidic Manipulation | Donglei (Emma) Fan, Ph.D., Associate Professor, Materials Science and Engineering Program, Department of Mechanical Engineering, University of Texas at Austin | The successful development of nanoscale machinery, which can operate with high controllability, precision, long lifetime, and tunable driving powers, are pivotal for the realization of future intelligent nanorobots, nanofactories, and advanced biomedical devices. However, the development of nanomachines remains one of the most challenging research areas, largely due to the grand difficulties in fabrication of devices with complex components and actuation with desired efficiency, precision, lifetime, and/or environmental friendliness. In this talk, I will discuss our recent breakthrough in innovative design, assembling and actuation of a new type of miniaturized rotary motors made from nanoscale building blocks, including nanowires and nanodisks. Arrays of nanomotors can be efficiently assembled and rotated with controlled angle, chirality and speed to 18,000 rpm, the same level of that of jet engine. The nanomotors have all dimensions less than 1 μm and are one of the smallest rotary Nanoelectromechanical System (NEMS) Devices. They can operate for 80 hours over 1.1 million cycles, the longest device lifetime that have been reported to the best of our knowledge. The nanomotors are further equipped with sensing capabilities into motorized nanosensors, which can actively tune biochemical release and monitor in real time, substantially enhance the efficiency of DNA removal, and manipulating flows in microfluidics. These results bring the great promises of nanomachines in biochemical and defense applications closer to reality. |
| October 21, 2016 | Magnetic Materials in the Spotlight of Polarized X-rays | Dr. Peter Fischer APS Fellow, IEEE Fellow | Acting Division Director, Materials Sciences Division, Lawrence Berkeley National Laboratory | Adjunct Professor in Physics, Physics Department, University of California, Santa Cruz | Nanomagnetism research which aims to understand and control magnetic properties and behavior on the nanoscale through proximity and confinement, is currently shifting its focus to emerging phenomena occurring on mesoscopic scales [1]. New avenues to control magnetic materials open up through enhanced complexity and new functionalities, which can impact the speed, size and energy efficiency of spin driven applications. A coherent scientific effort, which combines the design and synthesis of novel magnetic materials, exploiting e.g. the symmetry breaking arising from spin-orbit coupling at interfaces in heterostructures, theoretical modelling with advanced ab-initio approaches, and state-of-the-art magnetic characterization is mandatory to accomplish major breakthroughs. Magnetic soft X-ray spectro-microscopies [2] provide unique characterization opportunities to study the statics and dynamics of spin textures in magnetic materials combining X-ray magnetic circular dichroism (X-MCD) as element specific, quantifiable magnetic contrast mechanism with spatial (2D, 3D, and at interfaces) and temporal resolutions down to fundamental magnetic length and time scales. I will review recent achievements and future opportunities with magnetic spectro-microscopies at next generation x-ray facilities, such as X-ray free electron lasers and diffraction-limited storage rings. Examples will include the dynamics of magnetic skyrmions and vortex structures [3,4] with potential application to novel magnetic logic elements [5], magnetic spectromicroscopy of domain walls [6] with soft x-ray ptychography [7], and approaches to image the 3dim magnetic domain structures in rolled-up thin films with x-ray tomography [8]. This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05-CH1123 in the Non-Equilibrium Magnetic Materials Program. |
| October 14, 2016 | Year 5 Kick-off/State of the Center | Greg Carman, Center Director | Tom Normand, Director of Industrial Relations | Pilar O'Cadiz, Education Director | This presentation reviews TANMS progress over the past year and presents plans for the upcoming year in the areas of research, educational and industrial programs. The research portion describes testbed/research investments including research investments planned for the upcoming year as well as reviewing the TANMS supplemental funds awarded this year. The educational portion will discuss upcoming educational assignments as well as new educational programs. Finally, the status of our industrial advisory board (IAB) is presented with a focus on sustainability issues related to our 6th year review that will require significant increases in our IAB program. |
| August 26, 2016 | Publishing invoices using spintronics | Xavier Marti, Institute of Physics of the Czech Academy of Sciences; Owner and Chief Technical Officer at IGSresearch Ltd. | While I was a student and a post-doc, I got the feeling that spintronics was limited to data storage and random access memories. And so I was preparing my applications to start my senior academic career in 2013. I was aware that magnetic sensors had numerous applications but to some extend there was not enough “new research” to be done as to justify starting a new academic group. In this talk, I will walk through the business activities I took part in the past 3 years by which I fund some of my subsequent personal scientific research in spintronics using a couple of successful applications of magnetic sensors. A majority of scientists have a natural skill for managing large data sets, modelling and connecting the dots. In this talk, I will discuss the additional ingredients needed to turn this “mental integration ability and creativity” of scientists into invoices - the key paper. One often forgotten and misunderstood ingredient is the internet. It brings a tremendous additional value to any gadget simply because it is connected: One dollar becomes ten dollars, if the data flows properly into an iPad. On a more general frame, I will discuss how such small start-ups can be a feasible path to partially fund fundamental academic research. Scientific groups and its concomitant technology transfer departments operate nowadays in an imposed short-termism and, eventually, short-budgetism. For instance, It is very hard to achieve a significant success in revolutionizing the magnetic data storage market when, on one side, standard cycles are limited to 3~5 years and budgets to 1~5 million while the target is to attract the attention of 30 year old multinational companies. We will discuss several strategies that I have witnessed to tackle these challenges and I would like to brainstorm briefly on alternative paths and, specially, those ones which UCLA is currently following. |
| August 25, 2016 | Electrical switching of an antiferromagnet | Xavier Marti, Institute of Physics, Academy of Sciences of the Czech Republic, Czech Republic; IGSresearch Ltd., Spain | Louis Néel pointed out in his Nobel lecture that while abundant and interesting from theoretical viewpoint, antiferromagnets did not seem to have any applications. Indeed, the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization make antiferromagnets hard to control by tools common in ferromagnets. Strong coupling would be achieved if the externally generated field had a sign alternating on the scale of a lattice constant at which moments alternate in antiferromagnets. However, generating such a field has been regarded unfeasible, hindering the research and applications of these abundant magnetic materials. Theoreticians have recently predicted that relativistic quantum mechanics may offer staggered current induced fields with the sign alternating within the magnetic unit cell which can facilitate a reversible switching of an antiferromagnet by applying electrical currents with comparable efficiency to ferromagnets. Among suitable materials is a high Néel temperature antiferromagnet, tetragonal-phase CuMnAs, which we have recently synthesized in the form of single-crystal epilayers structurally compatible with common semiconductors. We demonstrate electrical writing and read-out, combined with the insensitivity to magnetic field perturbations, in a proof-of-concept antiferromagnetic memory device which operates USB-powered at room temperature. |
| April 1, 2016 | Tuning the Properties of Magnetic and Magnetoelectric Materials by using Solution-Phase, Nanoscale Structuring Methods | Shauna Robbennolt, PhD Candidate, UCLA Dept of Chemistry and Biochemistry | One of the major challenges facing TANMS is the development of materials optimized to meet the specific needs of the testbeds. The traditional approach to materials optimization in devices has been focused on tuning composition or film thickness, but the range of tunability in that case is limited. We aim to address these materials challenges by using solution-phase fabrication methods to control nanoscale architecture in addition to composition and thickness. This talk will overview these efforts and focus on three specific topics. (1) The first half of the talk will discuss the development of soft ferrite materials for use as the magnetostrictive layer in the multiferroic antenna. This work includes two materials systems: nanocrystalline cobalt ferrite (CFO) and thin film nickel zinc ferrite (NZFO). CFO is an promising material, but it is too magnetically hard for high frequency applications. By nanostructuring it we are able to tune its coercivity, remanence, and anisotropy field over a wide range. NZFO is a traditionally soft ferrite, but past efforts to make NZFO thin films have largely resulted in very lossy films due to imperfections in the films. Here we present a sol-gel route to fabricating high quality, low loss NZFO thin films. The second half of this talk will discuss the synthesis and deposition of monolayers of iron-containing intermetallic nanocrystals. (2) FePd nanocrystals are a promising material for use in charge-mediate memory devices due to its large voltage dependence of MCA. We have developed methods to synthesize FePd nanocrystals which offer a route to sub 10-nm bit size and we have been able to observe the VCMA effect in stacks containing a monolayer of these nanocrystals. (3) Finally, the Beloborodov group has used modeling to identify exchange interaction as an important, new type of magnetoelectric coupling in granular multiferroic composites. We are in the process of building test structures based on FePt nanocrystals to experimentally realize this type of coupling. Time permitting, this talk will briefly include the preliminary results from this effort. |
| March 4, 2016 | Quantitative characterization of acoustically-driven ferromagnetic resonance | Dominic Labanowski, UC Berkeley Electrical Engineering | In recent years, a novel technique for exciting ferromagnetic resonance using surface acoustic waves has been experimentally tested in materials as varied as nickel and dilute magnetic semiconductors. This acoustically-driven ferromagnetic resonance operates by coupling a traveling strain wave into a magnetoelastic ferromagnet to change its magnetocrystalline anisotropy in such a way as to drive it into resonance. In this talk I will discuss the methods used to obtain quantitative measurements of power consumption and efficiency in this system. We find the coupling of the surface acoustic wave into the ferromagnet can be highly efficient (> 99.9%), showing promise for extending acoustically-driven ferromagnetic resonance beyond its current use as a characterization technique into device applications. |
| February 26, 2016 | Micromagnetic Modelling on Mechanical/Spin Wave | Cai Chen, UCLA Mechanical and Aerospace Engineering | The semiconductor industry is facing enormous challenges because complementary metal-oxide semiconductor (CMOS) has reached physical limits in terms of feature size. Magnonic (spin wave based) devices can overcome this obstacle since the spin wave does not have significant thermal dissipation. However, classical approach to generate spin waves, e.g. current induced AC magnetic field, is energy inefficient and the induced magnetic field is non-localized, preventing miniaturization. Recently researchers have explored excitation of spin waves using magnetoelastic (ME) coupling in composite multiferroics, which is energy efficient. This presentation provides a numerical model to predict the response of a mechanically generated spin wave. The model uses a finite element approach to solve the fully coupled Landau–Lifshitz–Gilbert (LLG) equation with elastodynamics. Numerical results will be presented showing that a mechanically excited spin wave has a higher speed and lower attenuation compared with AC magnetic field generated spin waves. The results also show some interesting wave properties near the magnetoelastic resonance . These results strongly suggest that multiferroic generated spin waves are substantially superior to AC magnetic field generated spin waves. |
| February 19, 2016 | Integration and Packaging Strategies for Millimeter-CMOS Applications | Professor Rashaunda Henderson, University of Texas, Dallas | Millimeter-wave CMOS circuits are being developed for consumer products operating up to 100 GHz and beyond. As a result, silicon foundries have demonstrated promising transceiver circuits manufactured in a standard digital process flow as opposed to a higher cost RF back-end process. In addition to the transceiver design comes the need to provide packaging strategies and integration methods for interconnects and radiators in order to keep the systems low in cost and high in performance. This presentation focuses on the fabrication and integration of radiators used in two projects. One project focuses on broadband radiators for a 180-300 GHz spectrometer. The second project focuses on arrays used to generate orbital angular momentum. The fabrication, simulation and measurement of these radiators will also be presented. |
| February 12, 2016 | Salary Negotiation: How to Evaluate and Maximize Your Job Offer | Tom Normand, TANMS Director of Industrial Relations | This presentation will discuss the intricacies surrounding the negotiation and evaluation of a job offer specifically tailored to our TANMS Student Body including: •Information Gathering •Possible Offer Components •Preparation •The Differences Between Salary Discussion and Salary Negotiation •The Negotiation •Common Questions and Pitfalls •Tips for Success In addition, six relevant resource documents will be provided for future reference; A sample list of negotiable items, sample negotiation scripts, the specifics of negotiating a signing bonus, clarifying the offer, an offer evaluation worksheet, as well as a work satisfaction worksheet. |
| February 5, 2016 | TANMS Annual Reporting Requirements and Financials | Gregory Carman, TANMS Center Director | This seminar provides an overview of important dates and requirements pertaining to our upcoming annual review. In addition to the overview of the NSF Site Visit on May 17-18 and the Industrial Advisory Board Meeting on May 16, we will review the status of our current funding and additional monies available for the remainder of the budget period. Finally, we will discuss recruitment activities required for increasing the support for the antenna testbed. |
| January 29, 2016 | Engineering Nanoscale Multiferroic Composites for Memory Applications with Atomic Layer Deposition of Pb(ZrxTi1-x)O3 Thin Films | Diana Chien, Graduate Student Researcher, UCLA Dept of Chemical and Biomolecular Engineering | There are different types of coupling between mechanical, electrical, magnetic, and thermal properties that can be found in materials, which can be exploited for various applications. A multiferroic material is a material in which at least two ferroic forms co-exist. Specifically, when an electric field is applied magnetization is induced or when a magnetic field is applied polarization is induced. There are single-phase compounds that exist, but they have too weak of a magnetoelectric effect for device applications.Therefore, multiferroic composites need to be engineered, and they have been shown to have stronger magnetoelectric coupling which occurs through strain at the interface of ferroelectric and ferromagnetic layers that are coupled to each other. Presently, the goal for devices is to synthesize multiferroic composites that possess a strong ferroelectric and ferromagnetic coupling in order to control the magnetization by an electric field or the polarization by a magnetic field at room temperature. PZT is one of the best ferroelectric and piezoelectric materials known to date. Using atomic layer deposition (ALD), a surface-reaction controlled process based on alternating self-limiting surface reactions, an ultra-thin film of PZT can be synthesized with precise control of the elemental composition (Zr/Ti = 52/48) and film thickness. ALD provides much superior uniformity and conformality over complex surface structures with high aspect ratios. By controlling the composition, thickness, and conformality of ALD PZT thin films, multiferroic nanocomposites and memory devices were engineered. Specifically, ALD PZT thin films were shown to uniformly coat the walls of nanoscale porous CFO template to form a complex 3-D nanocomposite. The ME coupling effect was observed and suggests that porosity offers a promising complex multiferroic architecture. Additionally, ALD PZT films were integrated between MgO and CoFeB layers to fabricate PZT MTJs in order to increase the voltage-controlled magnetic anisotropy (VCMA) effect for memory applications. The PZT MTJs were measured to have tunnel magnetoresistance (TMR) of 53%, demonstrating a promising read-out process. The VCMA coefficient of PZT MTJs was ~40% larger than those of MgO MTJs. In conclusion, PZT MTJs were demonstrated to have tunneling magnetoresistance and an enhanced VCMA effect at room temperature, thereby being potential candidates for future voltage-controlled, ultralow-power, high-density memory devices. |
| January 22, 2016 | Magnetostrictive multilayers for actuators, sensors and magnetoelectric devices. | Nicolas Tiercelin, French National Centre for Scientific Research, LEMAC | After a brief presentation of the Institute of Electronics, Microelectronics and Nanotechnology (IEMN CNRS Lab. UMR8520) and our research group, I will give an overview of our research on nanostructured magnetostrictive multilayers and their applications. In particular, I will describe the properties of a field induced magnetic phase transition of the Spin Reorientation Type. In the vicinity of the SRT, the magnetoelastic sensitivity is dramatically increased and the response highly non-linear which can lead to original phenomena in the field of actuators, sensors and magneto-electric devices. |
| January 8, 2016 | Dynamic characterization of ferromagnetic thin films for strain-mediated multiferroic composites | Daniel B. Gopman, Materials Science and Engineering Division, NIST, Gaithersburg, MD | The high energy required to reverse the magnetization of ultrathin films presents a challenge to the development of energy-efficient data storage and spintronics applications. Magnetoelectric strain coupling has emerged as a promising method to lower the energy cost in operating these devices. Previous work has yielded a proof of concept for lowering the coercivity and the anisotropy of films (Co/Pt, CoFeB, Co/Pd) coupled to piezoelectric materials (PZT/PMN-PT) under applied electric fields [1-3]. Key to implementing strain-manipulation of magnetization in ultrathin films and patterned magnetic nanostructures is materials optimization for the properties needed for integration with the strain-mediating ferroelectric material. Recent investigations at the NIST Materials Science and Engineering Division have focused on understanding the dynamic magnetic properties of candidate magnetic thin films for composite magnetoelastic-piezoelectric composites using its suite of static and dynamic magnetic property characterization tools. In collaboration with researchers at UCLA, we have carried out the first broadband ferromagnetic resonance study of Gilbert damping and exchange stiffness in thin film Tb0.3Dy0.7Fe2 (Terfenol-D), a soft ferromagnetic material with the largest-known magnetostriction. We have also developed a high perpendicular magnetic anisotropy (PMA) Co/Ni multilayer (µ0HK > 0.25 T) with moderate Gilbert damping (0.02) compatible with direct sputtering onto a Pb[ZrxTi1-x]O3 (PZT) substrate. Under applied electric fields up to +/- 2 MV/m in the PZT, 0.05% in-plane compression of the magnetic multilayer can substantially reduce the PMA (µ0ΔHK ≥ 5 mT) and the coercive field (35%), demonstrating the significant magnetoelectric strain coupling in this new strain-mediated composite. |
| December 11, 2015 | Strain-mediated control of magnetism in micromagnetic structures | Hyunmin Sohn, Ph.D. Candidate, UCLA Dept of Electrical Engineering Sensors and Technology Laboratory | In this talk, we discuss our progress in the control of magnetism in microscale Ni rings. We demonstrate 45˚ rotation of magnetic onion state in Ni rings fabricated on PMN-PT substrates using photo-emission electron microscopy. We review the on-going efforts to achieve full 360˚ rotation with patterned surface electrodes that generate multi-directional in-plane strains. Preliminary experimental data of Ni structures on PZT substrates with surface electrodes are presented, which confirm the control of multi-directional in-plane strains. In addition, we briefly show fabrication results of Terfenol-D microstructures as a future replacement of Ni. |
| December 4, 2015 | Revealing the hidden structural phase of FeRh | Jinwoong Kim, Postdoctoral Fellow, Dept of Physics and Astronomy, CSU Northridge Nick Kioussis, Professor, Dept of Physics and Astronomy, CSU Northridge | FeRh undergoes a first-order magnetic phase transition from the G-type antiferromagnetic to the ferromagnetic phase that can be controlled by temperature, magnetic field, and/or strain. Recent experimental studies on FeRh films grown epitaxially on ferroelectric substrate have provided evidence of magnetic phase switch which is induced by the modulation of tetragonality. These results raise the intriguing question of the effect of strain on the relative stability of the various magnetic phases. In this study, using first principles total-energy electronic structure calculations we explored for the first time the effect of uniaxial strain on the stability of various magnetic structures of FeRh including the ferromagnetic, G- C-, and A-type antiferromagnetic (AFM) structures. In sharp contrast to previous theoretical and experimental reports that the cubic G-AFM is the ground state structure we demonstrate that this structure corresponds simply to a local energy minimum. We predict that (1) the tetragonal G-AFM corresponds to the global energy minimum which is lower than the cubic G-AFM by 2 meV/atom and (2) that the energy barrier between these two structures is only 1.2 meV/atom suggesting the transition between these structures at room temperature. The mechanical and thermodynamic properties of this energy landscape open interesting prospects for a novel memory device. |
| November 20, 2015 | Deterministic control of individual strain-mediated magnetoelectric elements | Jizhai Cui, Ph.D. Candidate, UCLA Mechanical and Aerospace Engineering | We developed two concepts for deterministic control of individual strain-mediated magnetoelectric elements, one by using patterned electrodes creating localized strain in various configurations, the other by designing magnetic elements in proper shape taking advantage of magnetic shape anisotropy. Finite element micromagnetic simulations were run for device design, followed by device fabrication and characterization on both bulk and thin film piezoelectrics. These concepts open a new design space for future nanoscale magnetoelectric devices, including non-volatile memory, logic and nanomotor systems. |
| November 13, 2015 | Scaling and characterizing multiferroic materials and technologies | Mark Nowakowski, Postdoc, UC Berkeley Electrical Engineering and Computer Science | In this talk I will discuss two multiferroic efforts underway at UC Berkeley. The goal of the first project is to demonstrate scalable and switchable exchange coupling between thin films of the single phase multiferroic BiFeO3 (BFO) and patterned nanodots of CoFe. The switching kinetics in this system are governed by ferroelectric domains in the BFO directly coupled to the CoFe magnetization; switching the FE polarization drives the magnet to reorient. Low energy 180° magnetic switching has already been demonstrated in this system in a micron-sized pattern where the switching of many FE domains (150 nm width) under a magnet triggers a switch. We seek to scale the switching behavior of this system to a single domain level and I will report on our progress. In the second half of my talk I will discuss a collaborative project between Berkeley and Cornell. In this work we simultaneously characterize the magnetoelectric coupling of a FeGa/PMN-PT composite multiferroic with magneto-optical and magneto-transport measurments. Initial results of this biaxial anisotropic system suggest it is highly sensitive to strain and may pave the way for a new low-energy, strain-based non-volatile memory. |
| November 6, 2015 | Progress in the Fabrication and Characterization of a Multiferroic Receiver Antenna | Paul Nordeen, Ph.D. Candidate, UCLA Dept of Mechanical and Aerospace Engineering | One of the most significant challenges facing the TANMS 2-D thrust is the development of accurate and high sensitivity radio frequency characterization techniques for the variety of multiferroic antennae being studied in our group. In this seminar a summary of the progression which has led to current testing and fabrication methodologies for magnetoelectric receivers developed within TANMS is outlined. Fabrication techniques for the current generation of SAW based antennae are presented along with a brief look at material selection. Current test results are discussed and compared to that of a linear piezomagnetic analysis with a focus on external bias field dependence. Potential issues regarding magnetic layer conductivity and measurement system noise are discussed as design challenges for the upcoming generation of the TANMS antenna. |
| October 30, 2015 | Anisotropic Strain Control of Magnetization in Ni and Terfenol-D Nanostructures | Kyle Wetzlar, Postdoctoral Researcher, UCLA Dept of Mechanical and Aerospace Engineering | Experiments and corroborating simulations are presented which show anisotropic magnetization modulation in thinfilms and nanostructures as a function of strain. Results from our collaborations with Brookhaven National Lab and the National Institute of Standards and Technology are presented. A case study of Lorentz Transmission Electron Microscopy (LTEM) is performed on a Ni thinfilm and various nanostuctures, each deposited on PMN-PT. A phase diagram is developed to discern the geometrically determined onion state formation in ring structures, the amount of strain which is transferred from the ferroelectric substrate to the nanoelements and the dynamic magnetic response of these structures as strain is controlled by bipolar voltage actuation. In addition to the results presented on Ni, preliminary findings for Terfenol-D thinfilms are presented which elucidate the magnetization dynamics, spinwave resonance (SWR) and exchange stiffness behavior in these small scale structures. |
| October 23, 2015 | Electric-field-controlled magnetic tunnel junctions for Magnetoelectric Random Access Memory | Cecile Grezes, Postdoctoral Researcher, UCLA Dept of Electrical Engineering | We review our progress in the development of magnetoelectric random access memory (MeRAM), based on electric-field-controlled writing in magnetic tunnel junctions (MTJs). MeRAM uses the tunneling magnetoresistance (TMR) effect for readout in a two-terminal memory element, similar to other types of magnetic random access memory (MRAM). However, the writing of information is performed by voltage control of the interfacial magnetic anisotropy (VCMA), as opposed to current-controlled (e.g. spin-transfer torque, STT or spin-orbit torque, SOT) mechanisms. Results are presented from a 1 Kb MeRAM test array. We report electric-field-induced switching with write energies down to 6 fJ/bit for switching times of 0.5 ns, in nanoscale perpendicular MTJs with diameters down to 50 nm. Write error rate, endurance and scaling of write voltage, speed and energy with junction diameter are presented. We also investigate the effect of in-plane magnetic fields on the memory performance. Finally, we discuss material-level requirements for the translation of MeRAM into mainstream memory applications. |
| October 16, 2015 | Integrated Multiferroics for Compact and Power Efficient Sensing, Memory, RF and Microwave Electronics | Hwaider Lin, Northeastern University | The coexistence of electric polarization and magnetization in multiferroic materials provides great opportunities for realizing magnetoelectric coupling, including electric field control of magnetism, or vice versa, through a strain mediated magnetoelectric coupling in layered magnetic/ferroelectric multiferroic heterostructures [1-8]. Strong magnetoelectric coupling has been the enabling factor for different multiferroic devices, which however has been elusive, particularly at RF/microwave frequencies. In this presentation, I will cover the most recent progress on new integrated multiferroic devices for sensing, memory, RF and microwave electronics, including novel RF NEMS magnetoelectric resonators with picoTesla sensitivity for DC magnetic fields, and novel GHz magnetic and multiferroic inductors with a wide operation frequency range of 0.3~3GHz, and a high quality factor of close to 20, and a voltage tunable inductance of 50%~150%. At the same time, we will demonstrate other voltage tunable multiferroic devices, including voltage tunable multiferroic bandpass filters, tunable bandstop filters, tunable phase shifters, magnetoelectric random access memory, etc. These novel integrated multiferroic devices show great promise for applications compact, lightweight and power efficient sensing, memory, RF and microwave integrated electronics. |
| October 9, 2015 | "TANMS State of the Center Address" | Gregory Carman, Center Director | This presentation provides an overview of the TANMS progress during the last three years as well as its focus for the next year. The presentation also includes important announcements for all of TANMS participants such as highlights of recent awards and honors. The update describes the ongoing search for an educational director as well as a discussions of adding new faculty. A portion of the presentation will describe the planned education program and the research focus for the upcoming year. |
| September 16, 2015 | Engineering Multiferroic Effects for Sensing Applications | Srinivas Tadigadapa, Pennsylvania State University | The interaction of elastically coupled magnetic and piezoelectric thin films constitutes a very complex domain of physics. This is mainly due to the simultaneous coupling of these phenomenon through the large matrices of elastic modulus, the piezoelectric, and magnetostrictive coefficients. Furthermore, in many cases these coefficients are not constants but a function ambient conditions such as temperature, stress and their gradients. In this talk we will explore some of the subtleties of these interactions and will demonstrate magnetometer concepts based upon sensitive exploitation of these concepts. Specifically this talk will discuss magnetometer concepts based on the magnetoelectric effect, the force-frequency effect in shear mode quartz resonators and the magnetoviscous effect of ferrofluids. |
| March 13, 2015 | NSF Site Visit Preparations | Greg Carman | This seminar provides important information to TANMS industries, faculty, postdocs, and students preparing for our renewal site visit April 27-29th. I will review the necessary meetings for our various constituencies taking place during the next month. These upcoming meetings are important to ensure our team speaks with one voice so that we are successful at our renewal year. If anyone has questions or concerns please bring them to the meeting to discuss. |
| March 6, 2015 | Multiscale modeling of composite multiferroics (Part II) | Oleg Udalov | We discuss magneto-electric (ME) coupling in composite multiferroics - materials consisting of ferromagnetic grains embedded into ferroelectric (FE) matrix. We propose ME coupling mechanism based on the interplay of Coulomb blockade effect, intergrain exchange interaction and FE properties and consider the problem at different length scales: 1) microscopic mechanism of ME coupling in composite multiferroics, 2) phenomenological (macroscopic) theory of the effect and 3) numerical modeling of composite multiferroics. In today's discussions we concentrate on phenomenological (macroscopic) theory. This is the Part II of our presentation. |
| February 27, 2015 | Multi-scale modeling of composite multiferroics | Oleg Udalov | In this report we will discuss magneto-electric (ME) coupling in granular multiferroics - materials consisting of ferromagnetic metal grains embedded into FE matrix. We propose ME coupling mechanism based on the interplay of Coulomb blockade effect, intergrain exchange interaction and FE dielectric properties. We consider the problem at different levels. We propose microscopic mechanism of ME coupling in composite multiferroics, develop phenomenological (macroscopic) theory of the effect and perform numerical modeling of granular multiferroics. |
| February 20, 2015 | Strain induced magnetic anisotropy switching in TbFe_2 | Ritika Dusad | Magnetostrictive materials change their shape upon application of strain and can be used as actuators and sensors. In this work, we perform a computational analysis of a highly magnetostrictive compound, TbFe2, to understand how the lattice and magnetization couple. We use Density Functional Theory (DFT) to investigate the magnitude and direction of the metallic moment as a function of pressure. The localized nature of Tb f-electrons classify this compound as ‘strongly-correlated’ and necessitate the simultaneous use of spin-orbit coupling to treat magnetostriction and the DFT+U methodology to capture the physics of the f-electrons. Although, the energy scales involved in spin-lattice interactions are extremely small, we were able to correctly reproduce the correct magnetic ground state and the experimentally observed ferrimagnetic coupling between Tb and Fe atoms in TbFe2. The easy axis in TbFe2 points along one of its body diagonals, which makes the shape of the crystal rhombohedral. Switching of magnetization between the easy axes requires the magnetization to pass through one of the [100] directions. In our study we show that by applying isotropic strain on TbFe2 crystal, we can decrease the energy barrier between [111] and [100] magnetization directions of the crystal. |
| February 13, 2015 | Strain-mediated 180 degree perpendicular magnetization switching for heterostructure based on LLG modeling | Xu Li | Current interest in magnetic thin film structures and superstructures like Cu/Ni/Cu sandwiches has led to the identification of a need for a better understanding of the effect of surfaces and interfaces on the magnetic behavior of materials. Theoretical calculations regarding surface effects on magnetic behavior are introduced in this work, based on which LLG equation was modified to include surface effects. Then FEM simulation of an epitaxial thin film Ni/Cu (001) has been performed to study the magnetic properties of Ni thin film as a function of thickness. Furthermore, based on surface effect 180 degree perpendicular switching can be achieved by precisely controlling in plane strain releasing time. This strain-mediated switching may provide a new method for next-generation memory device design. |
| February 6, 2015 | Atomic Layer Deposition of PZT Thin Films to Engineer Nanoscale Composites for Memory and Multiferroic Applications | Diana Chien | Lead zirconate titanate, Pb(Zr0.52Ti0.48)O3, exhibits strong coupling between electrical and mechanical energies, making it a promising material for piezoelectric microelectromechanical systems (piezoMEMS) and multiferroic nanoscale systems. In this work, ultra-thin PZT films were synthesized via ALD by depositing alternating layers of PbO, ZrO2, and TiO2 layers using organometallic precursors and H2O as the oxidant. By controlling the composition, thickness, and conformality of ALD PZT thin films, the properties of PZT can be exploited to increase the magnetoelectric (ME) coupling effect. In a 2D-2D structure, PZT was coupled with MgO/CoFeB to fabricate magnetic tunnel junction for ultralow-power voltage-controlled non-volatile memory devices. In a 0D-3D structure, ALD PZT thin films were shown to uniformly coat the walls of nanoscale porous CFO template to form a 3-D composite and a larger ME coefficient is expected due to an increase in surface area to volume ratio |
| January 30, 2015 | TANMS Annual Report Overview | Greg Carman | See abstract from 1/23/2015. |
| January 23, 2015 | TANMS Annual Report Overview | Greg Carman, Tsai-Tsai O-Lee | This seminar provides important information to TANMS faculty, postdocs, and students preparing for our third annual review. Attendance is mandatory. This third year review represents a critical assessment determining continued NSF financial support to TANMS for years 4-8. Success at this endeavor requires participation by our entire team paying particular attention to details in the upcoming months before the review week of April 27, 2015. This seminar presents requirements, information, and dates to ensure our team is successful in this effort. |
| December 12, 2014 | Strain-induced Giant Magnetoelectric Effect in Heavy Metal/Magnet/Insulator Junctions | Phuongvu Ong | The realization of the MeRAM is based on the voltage control of the interfacial magnetocrystalline anisotropy (MCA) of heavy-metal/ferromagnet/insulator (HM/FM/I) nanojunctions, where the non-magnetic HM contact electrode (Ta, Pd, Pt, Au) has strong spin-orbit coupling (SOC). Employing ab initio electronic structure calculations we have investigated the effect of electric-field (E-field) and epitaxial strain on the MCA of Ta(Au)/FeCo/MgO heterostructure. We predict that uniaxial strain leads to a wide range of interesting voltage behavior of the MCA ranging from linear behavior with positive or negative magnetoelectronic coefficient, beta, to non-monotonic ⋁-shape or inverse-⋀-shape E-field dependence with asymmetric beta’s. The calculations reveal that giant values of betas and E-field-driven magnetic switching can be obtained by tuning epitaxial strain. The underlying mechanism is the synergistic effects of strain and E-field on the orbital characters, the energy level shifts of the SOC d-states, and the dielectric constant of MgO. These results demonstrate for the first time the feasibility of highly sensitive E-field-controlled MCA through strain engineering, which in turn open a viable pathway towards tailoring magnetoelectric properties for spintronic applications. |
| December 5, 2014 | New Mechanism of Electro-magnetic Coupling in Composite Multiferroics | Igor Beloborodov | Composite multiferroics – materials with strong coupling between electric and magnetic degrees of freedom are the main topic of research in engineering and materials science. These materials show non-trivial fundamental physical properties and are promising candidates for numerous applications. In this talk I will discuss a new mechanism of magneto-electric coupling appearing in composite multiferroics due to the interplay of strong Coulomb interaction and ferroelectricity. This mechanism leads to the unusual magnetic phase diagram with the ordered magnetic phase appearing at higher temperatures than the magnetically disordered phase. The mechanism allows the electric field control of magnetic properties and magneto-transport in composite multiferroics. References: Phys. Rev. B 89, 174203 (2014) |
| November 21, 2014 | Bulk Acoustic Wave Mediated Multiferroic Antennas: Architecture and Performance Bound | Zhi Yao | Strain mediated multiferroic material have shown the promise of creating electromagnetic radiation through strain induced magnetization reorientation. As the first part of this talk, the bulk acoustic wave (BAW) based multiferroic antenna structure will be briefly reviewed. The second part of this talk will introduce three folds of efforts in modeling the BAW antenna structure, using one dimensional finite difference time domain method (FDTD): 1) strain mediated radiation with fixed value of permeability of the magnetostrictive material, showing a good radiation performance with high permeability and high energy coupling coefficient; 2) electric surface current driven radiation of a ferrite thin film, showing enhanced radiation at ferromagnetic resonance (FMR); 3) strain mediated radiation with FMR, showing an interfering behavior between FMR and acoustic resonance. The algorithm in the third modeling effort solves Maxwell’s equations, Newton’s laws and Landau-Lifshitz-Gilbert (LLG) equation simultaneously, and provides a fully dynamic view of this complicated physics. This is the advantage of this study. |
| November 14, 2014 | Reversible Electrically-driven Magnetic Domain Wall Rotation in Multiferroic Heterostructures to Manipulate Suspended On-chip Magnetic Particles | Mark Nowakowski | In this work, we experimentally demonstrate reversible electrically-driven, strain-mediated domain wall (DW) rotation in ferromagnetic Ni rings fabricated on piezoelectric [Pb(Mg1/3Nb2/3)O3]0.66-[PbTiO3]0.34 (PMN-PT) substrates. An electric field applied across the PMN-PT substrate induces a strain in the Ni ring structures producing DW rotation around the ring toward the dominant PMN-PT strain axis by inverse magnetostriction. We observe DWs reversibly cycled between their initial and rotated state as a function of the applied electric field with x-ray magnetic circular dichroism photo-emission electron microscopy. The DW rotation is analytically predicted using a fully coupled micromagnetic/elastodyanmic multi-physics simulation to verify that the experimental behavior is caused by the electrically-generated strain in this multiferroic system. Finally, this DW rotation is used to capture and manipulate magnetic particles in a fluidic environment to demonstrate a proof-of-concept energy-efficient pathway for multiferroic-based lab-on-a-chip applications. |
| November 7, 2014 | Nanostructured Cobalt Ferrite for the Multiferroic Antenna Application | Shauna Robbenolt | This talk will focus on using nanoscale structure to tune the properties of cobalt ferrite (CFO, CoFe2O4) with an emphasis on tailoring it to the multiferroic antenna application. The first portion will focus on tuning the coercivity and remanence of these films over a large range by precisely controlling the nanoscale architecture. This control is achieved by varying the precursor (nanocrystal vs sol gel), porosity and annealing temperature of the films. The second part will focus on independently controlling the saturation field of nanocrystal-based films, which is necessary for their use in the antenna application. Finally, if time allows I will introduce two new materials we are investigating for the antenna application, manganese-zinc and nickel-zinc ferrites. |
| October 31, 2014 | Actuation Mechanisms for Strain Mediated Magnetization Control | Abdon Sepulveda | An overview of strain mediated actuation mechanisms for magnetization control are introduced. Three basic models will be presented. First in-plane magnetization control for memory applications. For this, two models will be presented, a four electrode pattern configuration and a two electrode pattern. Advantages and disadvantages will be discussed. The second mechanism refers to ultra-thin films for which the magnetization vector has two stable states, both perpendicular to the plane of the film. An actuation mechanism that in which the magnetization is switched between the two stable equilibrium points will be presented. Finally a six pattern electrode configuration is used to prove the concept of continuous rotation for an onion state in nano-rings. This is the basis for nano-motors applications. Some other alternatives which are currently being developed will discussed. |
| October 29, 2014 | Multiferroics Short Course - Interface effects & Strain mediated magnetoeletric coupling in the presence of substrate constraint | Chris Lynch | Lecture 5, 45 minutes- Ferroelectric / Magnetostrictive domain wall interactions Charge effect on the MCA of FePd ultra thin laminates Surface contributions to MCA ; Lecture 6, 45 minutes (Jizhai’s work, Chuck’s work) Design example: Obtaining local strain using patterned electrodes (Jizhai and Josh’s work) Demonstration of local magnetization switching (tie back to memory testbed) |
| October 24, 2014 | Micromagnetic Model for Strain-mediated Multiferroics and Applications | Cheng-Yen Liang | Micromagnetic simulations of magnetoelastic nanostructures traditionally rely on either the Stoner-Wohlfarth model or the LLG model assuming uniform strain (and/or assuming uniform magnetization). While the uniform strain assumption is reasonable when modeling magnetoelastic thin films, this constant strain approach becomes increasingly inaccurate for smaller in-plane nanoscale structures. This presentation presents an analytical model to significantly improve simulation of finite structures by fully coupling LLG with elastodynamics and piezoelectric constitutive effects, i.e. the partial differential equations are intrinsically coupled. The coupled simulation method developed in this work along with Stoner-Wohlfarth model and LLG (constant strain) are compared to experimental data on nickel Ni nanostructures. Results reveal that this fully-coupled approach is significantly superior regarding agreement with experimental data. This more sophisticated modeling technique is also used for guiding the design process of future nanoscale strain-mediated multiferroic elements such as those needed in memory systems (strain-mediated memory) and in nano-ring devices. |
| October 22, 2014 | Multiferroics Short Course - Phase field modeling of Ferroelectrics, Magnetostrictives, and Magnetoelectric Laminates (cont'd) | Chris Lynch | Lecture 4, 45 minutes - Polarization as an order parameter and the TDGL equation Magnetization as an order parameter and the LLG equation |
| October 20, 2014 | Multiferroics Short Course - Phase field modeling of Ferroelectrics, Magnetostrictives, and Magnetoelectric Laminates | Chris Lynch | Lecture 3, 45 minutes - Basics of magneto-electro statics Potential energy of a dipole in a uniform field Material potential energy The linear dielectric problem by minimization of energy wrt polarization |
| October 19, 2014 | TANMS Perfect Pitch Competition | Student Leadership Council | |
| October 17, 2014 | Nanostructured Lead Zirconate Titanate for Continuous Magnetoelectric Composites | Abraham Buditama | We report on a nanoarchitectured, strain-coupled magnetoelectric composite which couple electric and magnetic polarization via stress mediation of piezoelectric lead zirconate titanate (PZT) and magnetostrictive cobalt ferrite (CFO), respectively. PZT was deposited by atomic layer deposition into a mesoporous CFO framework created by evaporation-induced self-assembly from a precursor solution templated by an amphiphilic diblock copolymer. The pores in this CFO thin film are 10–15 nm across and are filled with 3–6 nm of PZT. The intimate contact between the PZT inside the pores and the CFO pore walls allowed strain transfer between the two materials, and electrical poling of the system resulted in a change in magnetization along the out-of-plane direction of the film as measured by SQUID magnetometry. |
| October 15, 2014 | Multiferroics Short Course - Magnetoelectric phenomena at small length scales (cont'd) | Chris Lynch | Lecture 2, 45 minutes - The PMN-PT substrate (in-plane anisotropic strain) Demonstrated magnetic reorientation in nanostructures (overview of Tao’s work, others in Carman’s group using PMN-PT [011] and [001]) |
| October 13, 2014 | Multiferroics Short Course - Magnetoelectric phenomena at small length scales | Chris Lynch | Lecture 1, 45 minutes - Magnetization switching (Observations: MFM, MOKE, PEEM) Length scale transitions (MD-SD-SP) Strain mediated magnetoelectricity (fundamental equations and definitions) |
| October 10, 2014 | Large Resistivity Modulation in Mixed-Phase Metallic Systems | Yeonbae Lee | In numerous systems, giant physical responses have been discovered when two phases coexist, for example near a phase transition. An intermetallic FeRh system undergoes a first-order antiferromagnetic to ferromagnetic transition above room temperature and shows two-phase coexistence near the transition. We have investigated the effect of an electric field to FeRh/PMN-PT heterostructures and report 8% change in the electrical resistivity of FeRh films. Such a large electroresistance response is striking in metallic systems, in which external electric fields are screened and thus only weakly influence the carrier concentrations and mobilities. We show that our FeRh films comprise coexisting ferromagnetic and antiferromagnetic phases with different resistivities, and the origin of the effect is the strain-mediated change in their relative proportions. The observed behavior is reminiscent of colossal magnetoresistance in perovskite manganites, and illustrates the role of mixed-phase coexistence in achieving large changes in physical properties with low-energy external perturbation. |
| October 3, 2014 | TANMS Thrusts Progress Update: 1D, 2D, Modeling Thrusts | Pedram Khalili, Ethan Wang, Chris Lynch | |
| September 26, 2014 | TANMS Thrusts Progress Update: 3D and Materials Thrusts | Rob Candler, Sarah Tolbert | |
| September 19, 2014 | TANMS Industrial Affiliations Programs Update | Scott Keller | |
| September 12, 2014 | TANMS Education Program Update | George Youssef | |
| September 5, 2014 | TANMS State of the Center: Critical Third Year Review | Greg Carman | This presentation provides an overview of the TANMS program in the context of preparing for our 3rd annual review/renewal proposal. It is important to understand that this review (unlike previous reviews) represents a critical evaluation dictating future NSF support of the TANMS center, thus it affects the entire team’s funding. To prepare for the review, the NSF criteria as well as the threats identified by the NSF review team during our 2nd annual review is examined. Here it is critical to understand the criteria and correct the threats before our annual report submission (i.e. January 31, 2015 cutoff date). The annual report/renewal proposal includes a five year plan/proposal discussed in the context of a center wide roadmap suggested by the review team. Finally, this important review requires participation by the entire team, i.e. principal investigators, researchers, and students. I hope all will participate in this presentation/discussion to ensure that TANMS passes this critical third year milestone. |
| March 14, 2014 | TANMS Industry Affiliates Program Update | Scott Keller | Update from ILO regarding status of TANMS Industry Affiliates Program and plans for the upcoming year. |
| March 7, 2014 | Integrated Multiferroic Heterostructures and Low-Power Devices for Sensing, Power, RF and Microwave Electronics | Nian X. Sun | The coexistence of electric polarization and magnetization in multiferroic materials provides great opportunities for realizing magnetoelectric coupling, including electric field control of magnetism, or vice versa, through a strain mediated magnetoelectric interaction effect in layered magnetic/ferroelectric multiferroic heterostructures [1-7]. Strong magnetoelectric coupling has been the enabling factor for different multiferroic devices, which however has been elusive, particularly at RF/microwave frequencies. In this presentation, I will cover the most recent progress on novel layered microwave multiferroic heterostructures and devices, which exhibit strong magnetoelectric coupling. We will demonstrate strong magnetoelectric coupling in novel microwave multiferroic heterostructures. These multiferroic heterostructures exhibit a giant voltage tunable magnetic field of 3500 Oe, and a high electrostatically tunable ferromagnetic resonance frequency range between 1.75~ 7.57 GHz, a tunable frequency of 5.82 GHz or fmax/fmin=4.3 [2,3]. At the same time, we will demonstrate E-field modulation of anisotropic magnetoresistance, giant magnetoresistance and exchange bias at room temperature in different multiferroic heterostructures [4]. New multiferroic devices will also be covered in the talk, including ultra-sensitive nanoelectromechanical systems magnetoelectric sensors with picoTesla sensitivity [5], multiferroic voltage tunable bandpass filters[6], voltage tunable inductors [7], tunable bandstop filters, tunable phase shifters and spintronics, etc. |
| February 13, 2014 | Three Issues Related to YIG Spintronics | Mingzhong Wu | If a magnetic field is applied to a magnetic material, the field produces a torque on the magnetization of the material and drives it to precess. This precession is similar to the motion of a spinning top where the gravitational field produces a torque, instead of the magnetic field. It turns out that magnetization precession in yttrium iron garnet (YIG) decays slower than in any other known magnetic material. This fact gives rise to the recent birth of a new paradigm in the discipline of spintronics – “spintronics using yttrium iron garnets”. This talk will touch on several issues related to YIG spintronics. The presentation consists of three main parts. The first part will present on the feasibility of the use of sputtering, a technique widely accepted by industry, to grow low-damping, nanometer-thick YIG films. The second part will touch on the efficiency of spin angular momentum transfer across YIG/normal metal interfaces. The last part will report on the impacts of the magnetic proximity effect on spin pumping in YIG/Pt heterostructures. |
| February 7, 2014 | TANMS Director Presentation: Review, Funding and Retreat (RFR) | Greg Carman | |
| January 17, 2014 | Working with UCLA’s Office of Intellectual Property & Industry Sponsored Research (OIP-ISR) | Winston Lin (also reprsenting: Heather Felix, Scott Davis) | |
| December 6, 2013 | TANMS Talks 5 | Ramamoorthy Ramesh, Darrell Schlom, Sarah Tolbert, Craig Fennie, Abdon Sepulveda | |
| November 22, 2013 | TANMS Talks 4 | Jeff Bokor, Chris Lynch | |
| November 15, 2013 | TANMS Talks 3 | Igor Beloborodov, Jane Chang, Ethan Wang | |
| November 8, 2013 | TANMS Talks 2 | Ephrahim Garcia, Greg Carman, Rob Candler | |
| November 1, 2013 | TANMS Talks 1 | Kang Wang, Nicholas Kioussis, Sayeef Salahuddin | |
| October 25, 2013 | Magnetoelectric Memory Testbed: Overview, Requirements and Status | Pedram Khalili | This presentation will focus on the TANMS memory testbed. We will present the value proposition of voltage-controlled magnetoelectric memory in terms of energy efficiency, density, and scalability, and discuss the main performance parameters targeted by the testbed within TANMS. The material and device-level options being explored for realization of such a testbed, as well as their current development status and future plans will also be discussed. |
| October 18, 2013 | Phase-Field Modeling of Ferroelectric/Ferromagnetic Bilayer System: The Effect of Domain Structure on the Magnetization Reorientation | Dorinamaria Carka | Recent experimental investigations on magnetostrictive films deposited on ferroelectric substrates using optical polarization microscopy show that the underlying ferroelectric domain structure and its evolution under electric field can have a controlling effect on the ferromagnetic domain structure. Understanding the interaction and evolution of domain structures across the interface is of great importance for designing material systems with tunability and magnetoelectric control. We use the phase-field approach, which is suited for the investigation of multiferroic systems on the nanometer scale. This framework results in the TDGL equation to express the polarization relaxation in the ferroelectric phase and the LLG equation for the magnetization relaxation of the ferromagnetic phase. The constitutive response is expressed through a thermodynamic potential fitting the material properties such as the spontaneous and free strains, polarizations, magnetizations and the elastic, dielectric, magnetic properties. The resulting boundary value problem is implemented in COMSOL and solved using the finite element method. This model is used to investigate the effect of the ferroelectric domain structure and evolution on the ferromagnetic domain structure and magnetization reorientation. A bilayer material system representing a magnetostrictive layer such as Ni or GaFe grown on a BTO substrate is modeled to study the effect of equilibrium single crystal ferroelectric domain patterns on the imprinting of ferromagnetic domain structure with respect to the size of the magnetostrictive layer. Evolution of the ferroelectric domain structures under electrical loading and the effect on the magnetization control is also discussed. |
| October 11, 2013 | State of the Center | Greg Carman | |
| October 2, 2013 | New spintronics devices for GreenIT | Mathias Klaui | In our information-everywhere society IT is a major player for energy consumption and novel spintronic devices can play a role in the quest for GreenIT. Reducing power consumption of mobile devices by replacing volatile memory by fast non-volatile spintronic memory could also improve speed and a one-memory-fits-all approach drastically simplifies the microelectronic architecture design. The best-known memory device is the magnetic hard drive and here conventional magnetic fields are used to excite spin dynamics and manipulate magnetization as necessary for switching of magnetic bits. While this approach is now reasonably well understood and widely employed, it is an energy-hungry process leading to large power dissipation. Furthermore it entails limitations for the speed of magnetic switching as intrinsically the spin dynamics is limited by the precession frequency corresponding to the magnetic field. Novel low power storage-class memory devices have been proposed, where switching by alternative means, such as spin-polarized currents is used. We study the rich physics of the interaction between spin currents, photons and the magnetization, and we have used spin-polarized charge carriers and photons to excite spin dynamics and manipulate the magnetization on ultrafast timescales. We are probing the magnetization dynamics to gauge the ultimate speed limits of spin angular momentum transfer that governs device switching speeds. Finally using electric fields instead of currents might open novel avenues to ultra-low power switching of magnetization. |
| September 27, 2013 | Obtaining local strain in the presence of substrate constraint for nanoscale strain mediated magnetoelectricity | Chris Lynch | Strain mediated magnetoelectric coupling has potential applications in memory devices. The ability to switch the direction of magnetism using the anisotropic ferroelectric strain produced by domain engineering relaxor ferroelectric [011] cut and poled PMN-30PT has been demonstrated, but there is a barrier to implementation of this effect. The use of a large single crystal substrate to switch small magnetic islands on the surface switches all of the islands at once. Local control of magnetization through strain mediated magnetoelectric coupling requires localized control of strain. The ideal platform would be a ferroelectric film grown on a Si substrate with patterned magnetic islands on the surface that could be individually switched. Obtaining controllable local in-plane strain in a thin film ferroelectric has presented a number of challenges. These include the effects of the film structure itself (columnar grain structures, pores within grains, domain - grain boundary interactions, domain wall pinning by the electronic defect structure) and requirements of strain compatibility (the film is clamped by the substrate and local regions of the film are clamped by neighboring regions of the film). Finite element simulations have been used to generate electrode pattern designs that will enable local strain control. The resulting designs were fabricated and demonstrated to switch the easy axis of a Ni film at the mm scale. Fabrication work is ongoing to demonstrate this effect at the micron scale. |
| September 20, 2013 | Wave Propagation in Multiferroic Materials | Scott Keller | Multiferroic materials have been proposed for numerous applications in RF electromagnetic wave processing applications such as phase shifters and antenna facing materials. Here we discuss the behavior of wave propagation in multiferroic materials and how the magnetoelectric cross-coupling parameters impact the propagation modes. The means of producing this type of cross-coupling with available materials using piezoelectric and piezomagnetic layers is also discussed and one homogenization method to estimate cross-coupling parameters is presented. The overall properties of hybrid (homogenized piezoelectric/piezomagnetic) multiferroic materials is examined and the impact of the elastic coupling on the electromagnetic wave modes is further examined. |
| September 13, 2013 | Nanoscale Multiferroic Structures: Application, Measurement and Control | Rob Candler | There has been a resurgent interest in multiferroics based on the idea of stain-mediated indirect magnetoelectric (ME) coupling in ferroelectric and ferromagnetic materials. This stain-mediated coupling dramatically enhances ME coupling. High ME coupling is relevant for designing new multiferroic applications, such as miniature antennas, nanoscale memories, magnetic field sensors, and motors. This seminar presents the most recent experimental data of strain-induced reorientation of magnetism in nanoscale structures using photo emission electron microscopy. We will also discuss our ultimate goal, to deterministically control the magnetization of the structures via piezoelectrically-induced strain. |
| September 6, 2013 | Deterministic Control of Magnetization in Single-Domain Nanostructures | Abdon Sepulveda | Multiferroics is becoming a very attractive field due to the complex physics of these materials. Ferromagnetic, ferroelectric, and elastic effects are coupled in multiferroics. This opens a new way for developing novel technologies based on these multifunctional materials, such as sensors transducers memories and spintronic devices. In this seminar we will focus on the problems of controlling the magnetization in a ferromagnetic structure using strains as the control input. Three basic aspects of the problem are modeled and simulated using Finite Elements. First, results of a parametric study will be presented to show the effects of shape anisotropy. Angle and speed of rotation are mapped for different geometric parameters ands strains. The second problem is the controllability of a continuous magnetization rotation. A model consisting of a coupled Nickel dot on a piezoelectric substrate with imbedded electrodes to induce strains will be presented. Finally the third aspect of interest is controlling the position of the stable equilibrium points for the magnetization in the presence of an external bias magnetic field. |
| August 30, 2013 | Magnetic Topological Insulators: Materials, Physics and Engineering | Kang Wang | Topological Insulators have emerged recently with many existing new properties. I will introduce the history of TI research, leading to potentially low dissipation transport of quantum spin hall effect. I will present the magnetic doping to break time invariant symmetry, and many other new possibility have been predicted. I will describe our material effect at UCLA. |
| August 23, 2013 | Surface Acoustic Wave-Driven Ferromagnetic Resonance for Antenna Applications | Dominic Labanowki (and Sayeef Salahuddin) | As devices push towards further miniaturization, the design of novel antennas whose operating frequency is independent of size has become an area of great interest. Applications of this technology could range from enhancing current devices to enabling novel communications schemes (ie. chip-to-chip communication). In this talk I will focus on recent research using surface acoustic waves to drive nickel magnets into ferromagnetic resonance, as well as our plans to utilize this effect for antenna applications. More specifically, I will discuss our work on the numerical simulation of these structures, as well as preliminary designs for experimental measurements. |
| August 16, 2013 | Nanostructured Magnetoeletric Materials | Sarah Tolbert | This talk explores how nanoscale structure can be used to tune the properties of magnetoelectric materials. We consider both intrinsic and composite magnetoelectrics, asking how a combination of small size and mechanical flexibility can alter materials properties. We will first consider nanoporous bismuth ferrite (BFO) produced through wet chemical polymer templating routes. Porosity provides mechanical flexibility to this nanocrystalline oxide network, resulting in distortions of the idea rhombohedral architecture upon application of an electric field. This distortion produces significant changes in magnetization that are not observed on upon electrical biasing in either bulk or disordered nanocrystalline materials. We then turn to composite magnetoelectric materials, in this case using magnetoelectric coupling to tune the properties of superparamagnetic Ni nanocrystals. The results indicate that strain generated through a piezoelectric substrate can be used to tune the superparamagnetic-to-ferromagnetic transition temperature, providing a way to turn-on a net magnetization using an electric field. |
| August 9, 2013 | Deterministic Magnetization Control by Magnetoelastic Anisotropy: Memory and Motors | Joshua Hockel | Spintronic devices are of great interest today because they exhibit technologically useful emergent properties. For example, single domain magnetic random access memory (MRAM) is being investigated as a non-volatile alternative to traditional DRAM. However, writing to these magnetic devices remains a technical challenge due in part to the difficulty of generating local magnetic fields. A new device architecture, the magnetoelectric heterostructure, exhibits both a coexistence and coupling of ferromagnetic and ferroelectric ordering and enables magnetism to be manipulated with an electric field. In this talk, two magnetic devices are presented which are based on the magnetoelectric heterostructure concept: a 100 nm single domain magnetic memory device and a 2000 nm magnetic stator. In both devices, deterministic control of the magnetic phase is accomplished with electric fields applied to a piezoelectric substrate, with interfacial strain transfer playing the role of magnetoelectric energy transducer. In the memory device, the magnetization of the bit is rotated 90° following the application of an electric field. In the magnetic stator device, electric fields applied to patterned electrodes around a ring-shaped magnet create a time-stepped rotating magnetization, much like an electromagnetic motor. These devices demonstrate the viability of magnetoelectric heterostructures in future spintronic device research. Fabrication and characterization challenges will be discussed. |
| August 2, 2013 | Strain Mediated Multiferroics for Conformal Electrodynamics | Ethan Wang | Strain mediated composite multiferroics consisting of laminated piezoelectric and ferromagnetic material exhibits strong magnetoelectric coupling effect that is several order of magnitude than single phase multiferroic material. In this talk, we will explore dynamic effects in the multiferroic coupling between electromagnetic fields and mechanical fields. The enabling mechanisms and the performance limit of electromagnetic radiation out of thin film piezoelectric and piezomagnetic material are analyzed and discussed. Full-wave simulations based on finite-difference time-domain method are carried out to validate the proposed theory. It is concluded that the dynamic coupling between electromagnetic field and mechanical field in thin film strain mediated multiferroics can be used to develop a new class of antennas that are conformal, efficient and broadband. |
| July 26, 2013 | Static and time-resolved magnetic characterization by photoemission electron microscopy | Mark Nowakowski | The ambitious thrusts of TANMS require magnetic characterization on length scales which approach nanometers. We present our current investigations within TANMS to visualize magnetic contrast with resolutions ranging from microns to nanometers using a variety of techniques including the magneto- optic Kerr effect (MOKE) and x-ray magnetic circular dichorism-photoemission electron microscopy (XMCD-PEEM). Specifically, these techniques allow us to sense the voltage-controlled manipulation of magnetization states and domain walls in e-beam lithography patterned nano-rings and dots on piezoelectric substrates. Additionally, our group is developing methods to incorporate time-resolved capabilities which incorporate these unique visualization techniques. |
| July 19, 2013 | Synthesis and Integration of Multifunctional and Complex Oxide Materials | Jane Chang | The demand of engineering metal oxide thin films at an atomic level has grown immensely due to their versatile applications in numerous technologically advanced fields including microelectronics, optoelectronics, photonics, spintronics, energy storage devices and sensors. In this talk, I will discuss current research advances in atomic layer deposition for synthesizing multifunction and complex metal oxides with tailored electronic, chemical, interfacial, thermal properties and microstructures. Specifically, I will highlight our most recent research on the engineering of oxide thin films and their integration, for applications as multi-ferroic materials in memory devices, antenna and motors. |
| July 12, 2013 | Strain Mediated Multiferroic Nanostructures Testing and Modeling | Greg Carman | This presentation provides a brief overview of strain mediated composite multiferroic nanostructures conducted in Greg Carman’s group over the last few years including the recent work in TANMS. Experimental tests on Ni thin films show that both Bloch walls and Neel walls can be manipulated but results are ferromagnetic film thickness dependent. Experimental work on single domain Ni ellipses using PEEM measurement from Switzerland shows the magnetic domain can be reoriented 90 degrees but are dependent upon initial ferroelectric domain configurations. Analytical solutions directly coupling micromagnetics LLG with mechanical equilibrium shows superior correlation with experimental data than using Stoner Wolfarth or LLG with a constant strain assumption. Analytical results of coupled Maxwell’s equations with mechanical equilibrium indicate wave propagation is strongly coupled in a multiferroic for appropriate choices of material properties. A brief overview of the analytical models used to design a multiferroic receiver element that is subsequently fabricated and tested is described. |
| April 19, 2013 | New frontier in materials science: magnetic mesosolids seminar | Igor Beloborodov | |
| April 12, 2013 | Smart(er) Materials by Design seminar | Craig Fennie | |
| April 5, 2013 | Control Systems for Magnetic Micro-motors seminar | Ephrahim Garcia and Erick Ball | |
| March 22, 2013 | Spin Transport in Magnetic Tunnel Junctions seminar | Nick Kioussis | |
| March 15, 2013 | Multiferroic Materials Synthesis and Integration with Silicon seminar | Darrell Schlom | |
| March 8, 2013 | Electric Field Control of Magnetism | Ramamoorthy Ramesh | |
| March 1, 2013 | TANMS Student Leadership Council | Laura Schelhas and Joshua Hockel | |
| February 22, 2013 | TANMS Education | Rick Ainsworth and George Youssef | |
| February 15, 2013 | TANMS ILO | Scott Keller | |
| February 8, 2013 | TANMS 3-D Thrust | Rob Candler | |
| February 1, 2013 | TANMS 2-D Thrust | Ethan Wang | |
| January 25, 2013 | TANMS Materials Thrust | Sarah Tolbert | |
| January 18, 2013 | TANMS Modeling Thrust | Chris Lynch | |
| January 11, 2013 | TANMS 1-D Thrust | Pedram Khalili | |
| December 12, 2012 | TANMS Strategic Plan | Greg Carman |
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