Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Y54: Magnetic Devices and Applications |
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Sponsoring Units: GMAG Chair: Fazel Tafti, Boston College Room: Room 306 |
Friday, March 10, 2023 8:00AM - 8:12AM |
Y54.00001: 3D Random Magnetic Nanowire Network as Potential Neuromorphic Computing Element Dhritiman Bhattacharya, Erin L Marlowe, Thomas Hulse, James Malloy, Gen Yin, Kai Liu Interconnected magnetic nanowire (NW) networks can be the building blocks of 3-dimensional (3D) information storage and integrated neuromorphic computing platform. In this regard, we have previously shown discrete propagation of magnetic states driven by magnetic field and current in quasi-periodic 3D Co networks [1, 2]. In this study, we explore the possibility of utilizing random magnetic NW networks as neuromorphic computing elements. The NWs are synthesized via electrodeposition and sintered to form an interconnected network. Next, arrays of electrode pairs are fabricated to connect varying number of interconnected NWs. When magnetoresistance (MR) is measured between an electrode pair, multiple discrete jumps are observed due to domain wall pinning/depinning at the intersections, exhibiting step-by-step switching of the network. Each electrode pair shows unique MR feature as the number and geometry of NW interconnects vary between them. If this domain wall pinning/depinning is further controlled by applying current pulses of varying magnitudes, pulse-widths, or repetition numbers, synaptic weights could be diversely programmed by assigning different electrode pairs as inputs and outputs. This demonstration is a step towards integrating these 3D magnetic structures into artificial neural networks that can perform tasks such as pattern recognition. |
Friday, March 10, 2023 8:12AM - 8:24AM |
Y54.00002: Transport properties of superconducting - ferromagnetic nanowire devices Valentine Novosad, Tomas Polakovic, Timothy J Draher, Yi Li, John Pearson, Ulrich Welp, Zhili Xiao, Whitney R Armstrong, Zein-Eddine Meziani, Wai-Kwong Kwok The interplay between superconductivity and magnetism is interesting to basic science and applied physics. Here we propose to use the superconducting (SC) nanowires as an ultrafast probe of the magnetization dynamics, focusing on the vortex and antivortex spin state as a model system. While the vortex dynamics is well-studied and understood, the magnetic state described as an antivortex remains elusive and lacks experimental works owing to its metastability. In this work, we concidered elliptically shaped particles that can support single- and multi-vortex states. Using high-amplitude excitation at one of the eigenmode frequencies, we were able to induce a dynamic transition from a single vortex into vortex-antivortex-vortex (v-av-v) states. A newly formed state is stable in remanence and can be probed experimentally. To this end, we are developing SC nanowire devices integrated with magnetic particles. In our device, a lithographically defined sub-100nm NbN wire is biased close to its critical current Ic, where it loses superconductivity. An oscilating demagnetizing field of magnetic particle at its resonance interacts with Cooper pairs in the superconductor, exciting quasi-electrons that release their energy into the SC condensate through many inelastic collision processes. This results into the formation of a normal conducting hotspot roughly of the size of the coherence length, which diverts the supercurrent through the zero-resistance area around it. As the wire is biased close to Ic, the constricted area will exceed critical current densities and cannot persist in an SC state, which will cause a runaway annihilation of superconductivity until the whole wire cross-section turns normal. This process translates into an immediate spike in resistance with sub-10ps rise time, which triggers active or passive quenching that diverts the current from the wire and allows it to relax back into an equilibrium SC state. Once demonstrated experimentally, this approach can be used to characterize various nanomagnetic systems at low temperatures, including the v-av-v states as a function of the combination of the vortex core polarities and/or the excitation field direction. |
Friday, March 10, 2023 8:24AM - 8:36AM |
Y54.00003: Combinatorial logic devices based on a multi-path active ring circuit Alexander Khitun We describe a logic device in which an act of computation is associated with finding a path connecting input and output ports. The device is based on an active ring circuit comprising electric and magnetic parts. The electric part includes an amplifier, a phase shifter, and an attenuator. The magnetic part is a multi-port magnetic matrix comprising delay lines and frequency filters. Signals propagating on different paths may accumulate different phase shifts. Auto-oscillations occur in the circuit when the magnetic and electric parts match each other to meet the resonance amplitude and phase conditions. The system naturally searches for a resonance path that depends on the position of the electric phase shifter and amplification level. The path is detected by the set of power sensors. The proposed logic device can be used for solving a variety of computational problems. We present the results of numerical modeling illustrating prime factorization and finding the shortest path connected selected points on the mesh. We also present experimental data on the proof-of-the-concept experiment for the two-path device. The magnetic part consists of two waveguides made of single-crystal yttrium iron garnet Y3Fe2(FeO4)3 (YIG) films. Different phase shifts per delay line are achieved by adjusting the magnitude and direction of the bias magnetic field. The auto-oscillation signal changes the propagation path in the magnetic matrix depending on the position of the outer electric phase shifter. The power difference between the active and passive paths exceeds 40 dBm at room temperature. The described logic devices are robust, deterministic, and operate at room temperature. The number of possible paths increases factorial with the size of the mesh. It may be possible to encode information in paths and retrieve it using the external phase shifters and attenuators. Potentially, combinatorial logic devices may compete with quantum computers in functional throughput. Physical limits and constraints are also discussed. |
Friday, March 10, 2023 8:36AM - 8:48AM |
Y54.00004: Non-Reciprocity and Non-linearity in Engineered Magneto-Acoustic Devices Michael R Page, Derek Bas, Piyush Shah, Roman Verba, Serhiy Leontsev, Alexei Matyushov, Michael Newburger, Nian X Sun, Vasyl S Tyberkevych, Andrei N Slavin, Abbass Hamadeh, Philipp Pirro, Mathias Weiler Nonreciprocity, the property of merit for a variety of RF components such as isolators and circulators, is typically difficult to achieve with the magnitude required for applications. Many systems which demonstrate non-reciprocity are not suitable for scaling to the size, weight, and power required for applications, or do not exhibit a sufficient intensity of the effect for applications relevance. One such physical system which generally does not exhibit non-reciprocity is that of acoustic waves. I will discuss discoveries of non-reciprocity and non-linearity in surface acoustic waves interacting with magnetic materials. Giant Nonreciprocity of 48.4 dB (ratio of 1:100,000) is achieved in the transmission of surface acoustic waves on a lithium niobate substrate coated with ferromagnet/insulator/ferromagnet (FeGaB/Al2O3/FeGaB) multilayer structure. This same structure has now also demonstrated very large phase shifts due to a similar interaction, and the nature of the magnetic ordering and coupling to the acoustic system will be discussed. Nonlinearity will also be discussed and is demonstrated using focused interdigitated transistors employing curved fingers, in contrast to the straight fingers typically used. These transducers are engineered to concentrate acoustic energy towards a small region in the center of the device allowing driven magnetic precession much higher than was previously possible. Enhanced acoustic absorption and modeling of the response will be shown. These devices promise functionality which outperforms current state of the art high frequency devices in a novel acoustic wave system that facilitates unprecedented size, weight, and power reduction. |
Friday, March 10, 2023 8:48AM - 9:00AM |
Y54.00005: CMOS + stochastic MTJ: Heterogeneous p-computers for energy-based machine learning Keito Kobayashi, Qixuan Cao, Nihal Singh, Kemal Selcuk, Tianrui Hu, Shaila Niazi, Navid A Aadit, Shun Kanai, Hideo Ohno, Shunsuke Fukami, Kerem Y Camsari The nearing end of Moore's Law led to the rise of domain-specific hardware to extend capabilities of existing CMOS technology. Probabilistic computing with p-bits has emerged as a promising computing platform, naturally applicable to probabilistic models and algorithms [1,2]. Here, we present an experimental demonstration of a heterogeneous computer where stochastic Magnetic Tunnel Junctions (sMTJ) are connected to conventional Field Programmable Gate Arrays (FPGA). The sMTJs drive a large number of digital p-bits in the FPGA by providing asynchronous and truly random bits. We show how this platform can be used to train a class of physics-inspired, energy-based Machine Learning models. Compared to purely digital and pseudorandom number generators (PRNG), augmenting the FPGA with the truly random bits from the sMTJs increase the quality of randomness, resulting in superior performance in learning, while decreasing the area footprint and energy consumption needed from PRNGs. Our results highlight the promise of repurposing embedded magnetic memory technology to design energy-efficient and scalable CMOS + X architectures. |
Friday, March 10, 2023 9:00AM - 9:12AM |
Y54.00006: Nanoscale magnetic field sensing with spin-Hall nano-oscillator devices Yanyou Xie, Hil Fung Harry Cheung, Gregory D Fuchs Spin-Hall nano-oscillators (SHNOs) are magnetic bilayer devices that convert dc charge current to microwave frequency magnetic oscillations under external magnetic field. The operational principle is based on spin Hall effect: a charge current in a nonmagnetic layer with spin-orbit interaction generates a transverse pure spin current that flows into an adjacent magnetic layer and compensates its magnetic damping. This leads to auto-oscillations in the gigahertz frequency regime. The oscillation frequency of SHNOs is tuneable with dc current and external magnetic field, enabling their applications as agile microwave signal generators. Here we investigate their application as nanoscale magnetic field sensors. We fabricated SHNO devices based on Ni81Fe19/Au0.25Pt0.75 with a single 150 nm constriction and four 150 nm constrictions in an array separated by 350 nm. These devices are designed to operate in a bias field of ~400 Oe in the sample plane. The 1-constriction device has a detectivity below 1 μT/√Hz for ac magnetic field frequency > 100 Hz (Figure 3) with an effective sensing area of 0.071 μm2. The 4-constriction device has a detectivity below 1 μT/√Hz for ac magnetic field frequency > 20 Hz, but with a slightly larger effective sensing area of 0.32 μm2. The devices are able to sense small magnetic field variation around the bias field in both time and frequency domain. The nanoscale sensing area of these devices is interesting for local sensors such as in scanning probe magnetometry. |
Friday, March 10, 2023 9:12AM - 9:24AM |
Y54.00007: Impact of ferromagnetic grains on nanowire spin torque oscillators Prakash Bissokarma, David Lempke, Christopher Safranski, IIya N Krivorotov, Eric A Montoya Spin-orbit torques in bilayers of ferromagnetic and nonmagnetic materials hold promise for energy efficient nanodevices. Particularly, spin torque oscillators provide for compact tunable microwave sources and have potential application in neuromorphic computing. In this presentation, we investigate the impact of granular media on spin torque oscillator dynamics. We demonstrate that nominally identical wires can exhibit drastically different oscillatory behavior - differing in emission spectra and critical currents. Spin torque ferromagnetic resonance measurements reveal vastly different mode structures for the devices. Using micromagnetic simulations, we qualitatively reproduce the experimentally observed mode structure by accounting for granularity in the ferromagnetic layer that includes weakened intergrain exchange coupling and variations in perpendicular magnetic anisotropy. Our results show that disorder in ferromagnetic materials can significantly impact spin torque oscillator performance. |
Friday, March 10, 2023 9:24AM - 9:36AM |
Y54.00008: Optimising the outcome of the high-throughput search for rare-earth-free permanent magnets Alena Vishina, Olle Eriksson, Heike C Herper With the exponential growth in the number of electric vehicles and windmills required for the transition to green energy, there is an ever-increasing demand for permanent magnets (PM). However, all the materials used in these applications nowadays contain rare-earth (RE) elements, which are expensive and mined with techniques damaging for the environment. |
Friday, March 10, 2023 9:36AM - 9:48AM |
Y54.00009: Crucial role of phase competition and spin-lattice relaxation in gigantic switchable optomagnet effect of (Fe0.875Zn0.125)2Mo3O8 Yao-Hua Zhuang, Heng-Wei Liu, You Hua Li, Takashi Kurumaji, Yoshinori Tokura, Yu Miin Sheu It has been discovered that crystal field excitations with spin-flip transition is a key to control switchable optomagnet effects in antiferromagnetic (Fe0.875Zn0.125)2Mo3O8. However, when the flipped spins are in excited states to frustrate the balanced spin moments, the photoinduced magnetization has not occurred yet. Only after ultrashort pulses disappears does the gigantic magnetization starts to grow from zero moment. To construct a detailed picture of crystal field excitation, we design the experiment to compare cases between Néel axis perpendicular and parallel to the angular momentum of circularly polarized light. With aids of Kerr effect microscopy and applications of magnetic field, we uncover all indispensable factors for the gigantic optomagnet effect and discern photoinduced switchable magnetization from non-switchable demagnetization. Our experimental designs, while rarely explored, is critical for developments of antiferromagnetic memory devices using insulating oxides. |
Friday, March 10, 2023 9:48AM - 10:00AM |
Y54.00010: Electrical Detection of Short-Wavelength Nonreciprocal Magnons in Magnetic Thin Film Device Yi Li, Tzu-Hsiang Lo, Jinho Lim, Jiangchao Qian, Zhihao Jiang, John Pearson, Ralu Divan, Wei Zhang, Andre Schleife, Wolfgang Pfaff, Jian-Min Zuo, Ulrich Welp, Wai-Kwong Kwok, Axel Hoffmann, Valentine Novosad Magnons possess nonreciprocity with multiply mechanisms and can reach ultra-small wavelength down to nanometer scale at microwave frequency excitations, they can be utilized for developing miniaturized and chip-embedded microwave isolation components for advanced information processing. Up to now, high performance of magnon isolation in magnetic thin-film devices is still demanding for practical applications. |
Friday, March 10, 2023 10:00AM - 10:12AM |
Y54.00011: Determining switching exponents with stochastic magnetic tunnel junctions Shun Kanai, Takuya Funatsu, Jun'ichi Ieda, Shunsuke Fukami, Hideo Ohno The stability of physical systems under external perturbation is often described by local bifurcation and/or switching exponents, and access to them is essential to establish the reliable operation of solid-state devices. We investigate the exponents of spin transition torque (STT) and perpendicular magnetic field H in nanoscale magnetic tunnel junctions (MTJs) with a perpendicular easy axis [1]. By combining three dynamical measurements in a stochastic MTJ, we experimentally determine the switching exponents, which have not been experimentally accessed before [2]. |
Friday, March 10, 2023 10:12AM - 10:24AM |
Y54.00012: Measuring spin torque efficiencies in Pt/ferromagnetic insulator bilayers with spin-torque ferromagnetic resonance Sanyum Channa, Xin Yu Zheng, Zbigniew Galazka, Haowen Ren, Tian-Yue Chen, Andrew D Kent, Yuri Suzuki, Daisy O'Mahoney Low damping ferromagnetic insulators (FMI) when interfaced with heavy metals (HM) like Pt can be manipulated using spin-orbit torques (SOT), hence making them a key building block for efficient spin-based electronics due to their minimization of dissipative charge currents. However, most studies on HM/FMI bilayers report low spin torque efficiencies of θ = 0.01-0.1, which makes the future of FMI-based devices unclear. Recently, we demonstrated highly efficient SOT switching in a novel spinel FMI Li0.5Al1.0Fe1.5O4 (LAFO) when interfaced with Pt, with switching current densities ~106 A/cm2. This was a result of the carefully engineered Pt/LAFO interface that yielded a large θ = 0.57 from second harmonic measurements. In this talk, we present complementary results by studying the charge-to-spin interconversion in the Pt/LAFO system using spin-torque ferromagnetic resonance (ST-FMR). By analyzing the evolution of the ST-FMR lineshapes over a series of Pt/LAFO samples, we extract the spin torque efficiency and compare them with values determined previously through second harmonic measurements and other equivalent techniques. |
Friday, March 10, 2023 10:24AM - 10:36AM |
Y54.00013: Machine-learning-guided discovery and experimental synthesis of rare-earth-free magnetic ternary compounds Weiyi Xia, Cai-Zhuang Wang, Masahiro Sakurai, Balamurugan Balasubramanian, Timothy Liao, Huaijun Sun, Chao Zhang, Renhai Wang, Kai-Ming Ho, James R Chelikowsky, David J Sellmyer Magnetic materials are essential for energy generation and information devices, and they play an important role in advanced technologies and green energy economies. Currently, the most widely used magnets contain rare earth (RE) elements. An outstanding challenge of notable scientific interest is the discovery and synthesis of novel magnetic materials without RE elements that meet the performance and cost goals for advanced electromagnetic devices. Here, we report our discovery and synthesis of an RE-free magnetic compound, Fe3CoB2, through an efficient feedback framework by integrating machine learning (ML), an adaptive genetic algorithm, first-principles calculations, and experimental synthesis. Magnetic measurements show that Fe3CoB2 exhibits a high magnetic anisotropy (K1 = 1.2 MJ/m3) and saturation magnetic polarization (Js = 1.39 T), which is suitable for RE-free permanent-magnet applications. Our ML-guided approach presents a promising paradigm for efficient materials design and discovery and can also be applied to the search for other functional materials. |
Friday, March 10, 2023 10:36AM - 10:48AM |
Y54.00014: Magnetic Anisotropy Modulation in Bismuth Substituted Yttrium Iron Garnet with Voltage Controlled Strain Walid Al Misba, Kensuke Hayashi, Miela Josephine Gross, Daniel B Gopman, Caroline A Ross, Jayasimha Atulasimha Voltage control of spintronic devices can lead to extremely energy efficient computing in intelligent edge devices and future IoTs [1,2]. In our previous study we reported voltage induced strain mediated modulation of perpendicular magnetic anisotropy (PMA) in Yttrium substituted dysprosium Iron garnet (Y: DyIG) [3]. In this study, we perform magnetic anisotropy modulation in Bismuth substituted Yttrium Iron Garnet (Bi: YIG) with voltage induced strain. A 55 nm thick Bi:YIG film is grown on piezoelectric PMN-PT/SiO2 (5 nm) where the SiO2 layer is used to prevent the heterostructure templating from perovskite. Further the ratio of Bi:Y is optimized for low coercivity. The piezoelectric is poled along [011] direction by applying voltages across the thickness of PMN-PT/SiO2/Bi-YIG heterostructure. Changes in magnetic anisotropy in poled heterostructure for different amplitude voltages will be studied in-situ with magneto-optical Kerr microscopy (MOKE). |
Friday, March 10, 2023 10:48AM - 11:00AM |
Y54.00015: Investigation of MnBi-based composite magnets Parashu R Kharel, Gavin M Baker, Manish Neupane, Tula R Paudel Rare-earth-free permanent magnet materials have attracted much attention due to a limited supply and high price of the rare-earth metals used in current high performance magnets. MnBi and MnBi-based materials have been investigated as prospective rare-earth-free permanent magnets with moderate energy product. We have synthesized Mn55Bi45Cx magnet using arc melting and high-vacuum annealing. The composite magnets Mn55Bi45Cx-Fe and Mn55Bi45Cx-Co were prepared by grinding Mn55Bi45Cx with commercially available Fe and Co nanoparticles using mortar and pestle. The room temperature x-ray diffraction patterns indicate that Mn55Bi45Cx crystallizes in the hexagonal NiAs-type structure. The high-field (3T) magnetization measured at room temperature for Mn55Bi45Cx is 60 emu/g and that for Mn55Bi45Cx:Fe (10:1) is 71 emu/g consistent with the theoretical prediction. The coercivity measured at 300 K for Mn55Bi45Cx and Mn55Bi45Cx:Fe are 17 kOe and 9.0 kOe, respectively. In this presentation I will also discuss the data collected on Mn55Bi45Cx-Co samples. |
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