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 W54: Skyrmion Based DevicesFocus
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Sponsoring Units: GMAG Chair: Hamed Vakili, University of Nebraska - Lincoln Room: Room 306 |
Thursday, March 9, 2023 3:00PM - 3:36PM |
W54.00001: Controlling Creation, Annihilation, and Movement of Magnetic Skyrmions Studied by Soft X-ray Microscopy Invited Speaker: Mi-Young Im Skyrmions are spatially localized quasiparticle-like topological structures. Massive interests have been attracted to skyrmions because of their non-trivial topological properties that triggers intriguing physical phenomena and their high potentials in a wealth of technological applications. Their nanoscale size, superior stability, purported efficient coupling to electrical currents, energy efficient operation in CMOS-compatible metallic thin films promise skyrmion-electronics toward next-generation novel memory, logic, and neuromorphic/reconfigurable computing applications [1]. |
Thursday, March 9, 2023 3:36PM - 3:48PM Author not Attending |
W54.00002: Precise transport of skyrmions by surface acoustic waves Jintao Shuai, Luis Lopez-Diaz, John E Cunningham, Thomas A Moore Skyrmions are topologically protected chiral spin structures showing great potential for the next generation of data storage and processing devices[1]. However, controlling such chiral spin textures efficiently and precisely remains unsolved. Here, we demonstrate the precise transport of skyrmions by surface acoustic waves using micromagnetic simulations (Mumax3) [2]. The skyrmion was initialised at different positions along the nanotrack. Results showed that with the application of the standing SAW, the skyrmion did not move if its initial position was at the antinodes of the standing SAW. Whereas starting from a node, the skyrmion did move towards the closest anti-node of the standing SAW indicating that the strain gradient is the origin of the SAW-driven skyrmion motion[3]. The skyrmion moves continuously in the presence of the travelling SAW regardless of its initial position with a higher velocity (2.39 cm/s) than that of the standing SAW-induced skyrmion motion. This is due to the travelling SAWs providing a constant driving force to the skyrmion. The skyrmion also moves in the vertical direction owing to its chirality. Orthogonal SAWs (horizontal travelling SAW and transverse standing SAW) were then applied to the skyrmion, which can drive skyrmion horizontal motion and pin the skyrmion in the desired trajectory. Results showed that in the presence of orthogonal SAWs, the skyrmion moved along the centre of the nano-track with very limited vertical motion. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W54.00003: The Effect of Polycrystallinity on Skyrmion Logic Devices Mehmet Cengiz Onbasli, Arash Mousavi Cheghabouri, Ferhat Katmis Polycrystallinity commonly occurs in magnetic thin films but the effect of polycrystallinity on magnetization dynamics and its equilibrium is not considered in micromagnetic models. Polycrystals structures mathematically exist as Voronoi tessellation patterns. Each grain possesses distinct magnetic parameters such as saturation magnetization (Ms), uniaxial magnetic anisotropy (Ku1) and preferred magnetization orientations. Here, we investigate the impact of Voronoi-type polycrystallinity in different magnetic material parameters on the equilibrium magnetization. We find that these variations do not hinder the operations of magnetic logic and memory devices with non-trivial geometry and rich interactions. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W54.00004: All-electrical reading and writing of spin chiralty Fan Li, Yicheng Guan, Peng Wang, Zhong Wang, Chi Fang, Ke Gu, Stuart Parkin Spintronics promises new data encoding and computing technologies. Spin chirality plays a very important role in the properties of many topological and non-collinear magnetic materials. Here we propose the all-electrical detection and manipulation of spin chirality in insulating chiral antiferromagnets. We demonstrate that the spin chirality in insulating epitaxial films of TbMnO3, can be read electrically via the spin Seebeck effect, and can be switched by electric fields via the multiferroic coupling of the spin chirality to the ferroelectric polarization. Moreover, multi-valued states of the spin chirality can be realized by the combined application of electric and magnetic fields. Our results are a path towards next-generation, low-energy consumption, memory and logic devices that rely on spin chirality. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W54.00005: Skyrmion Motion in Channels with Engineered Dzyaloshinskii-Moriya Interactions Jacob B Freyermuth, Denis Pelekhov, Po-Kuan Wu, Roland K Kawakami, Mohit Randeria Fast and efficient current-driven manipulation of skyrmions is vital for future design of skyrmion-based memory devices. Given this, it is important to find ways to increase the velocity that skyrmions can move when driven by current. We consider both spin transfer torque and spin orbit torque drives. We report on a proposed device geometry that makes use of spatial variation of the strength of the Dzyaloshinskii-Moriya interaction to greatly increase the maximum velocity that the skyrmion can achieve in the channel. We also investigate the relationship between skyrmion size and velocity when driven by current. Using a combination of simulations and analytical formulas, we show that the skyrmion motion in our proposed geometry can lead to a several times increase in the maximum achievable skyrmion velocity as compared to a physical narrow channel device. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W54.00006: Reservoir Computing with Spin Waves in a Skyrmion Crystal Mu-Kun Li, Masahito Mochizuki Skyrmions in chiral magnets are nanometric spin textures characterized by a topological invariant and often emerge as a skyrmion crystal in a magnetic field. We propose that skyrmion crystals possess high potential for reservoir computing, one of the state-of-the-art derivatives of recurrent neural networks. Benefited from the nonlinear interferences and slow relaxations of spin waves propagating in the crystal, the skyrmion reservoir attains several fundamental requirements of reservoir computing, e.g., the generalization ability, short-term memory, and nonlinearity. We demonstrate these properties by performing three standard tasks, i.e., the input-estimation task, short-term memory task, and parity-check task on the skyrmion reservoir. We then extend our study to more nontrivial tasks, including the nonlinear autoregressive moving average task and handwritten digit recognition task. A low mean square error can be achieved, and a digit recognition rate as high as 95% can be reached by the skyrmion crystal with the number of virtual nodes being less than four hundred, consolidating the practical potential of the skyrmion reservoir. Since skyrmion crystals emerge spontaneously in a static magnetic field, the skyrmion reservoir requires no advanced nanofabrication for production, in contrast to other proposed magnetic reservoirs, e.g., spin-torque oscillators. Our work is expected to realize a breakthrough in the research of spintronics reservoir computing. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W54.00007: Demonstration of a thickness-step Skyrmion Injector in FeGe Murray Wilson, Geetha Balakrishnan, Peter D Hatton, Luke A Turnbull, Samuel H Moody, Matthew T Littlehales, Raymond Fan, Paul Steadman Magnetic skyrmions have attracted significant research interest over the past decade, both for their intrinsically interesting physical properties, and for their potential as information carriers in novel computing devices [1]. FeGe is one example of a material that hosts skyrmions, which is particularly useful as a test case for skyrmionic devices as the skyrmions are found near room temperature [2]. For any skyrmionic device to prove useful, a reliable method of injecting and removing skyrmions from a defined region of the material is needed. We report the demonstration of such a a skyrmion injector device utilizing electrcic currents applied across a thickness step in FeGe lamella. Our measurements show that in certain temperature and field conditions, skyrmions can be reversibly injected from a thin region of an FeGe Lamella where they exist as an equilibrium state, into a thicker region, where they can only persist as a metastable state. This injection is achieved with a current density of 3 x 108 A / m2 which is small relative to the currents required to move magnetic domain walls, and viable for electronic applications. This injector could be used for injecting or removing small numbers of skyrmions into a defined region of a skyrmion hosting material for further manipulation in devices such as skyrmion racetrack memory or reservoir computing, and therefore paves the way for potential future skyrmion applications. |
Thursday, March 9, 2023 4:48PM - 5:00PM Author not Attending |
W54.00008: Current induced magnetization switching of thick antiferromagnet and ferromagnet by Seeded Spin-Orbit Torque Binoy Krishna K Hazra, Banabir Pal, Börge Göbel, Jae-Chun Jeon, Prajwal R Madhusudan Rao, Hakan Deniz, Holger Meyerheim, Ingrid Mertig, See-Hun Yang, Stuart Parkin One of the most exciting quests in spintronics is the discovery of more efficient current-induced torques for setting distinct magnetic states. In this regard, the well-established spin-orbit torque switching of magnetization has huge scientific and technological impact. However, short spin-diffusion lengths make it possible to switch only thin magnetic layers which, therefore, typically suffer from a lack of thermal stability. Here we report a novel Seeded Spin-Orbit Torque which sets the magnetic states of even thick layers of the chiral kagome antiferromagnet Mn3Sn. This mechanism involves setting the orientation of the antiferromagnetic domains in a thin region at the interface of the Mn3Sn with a heavy metal layer. This interface region seeds the resulting spin texture of the entire layer, and thereby overcomes the thickness limitation of conventional spin-orbit torques. Further, we show that this Seeded Spin-Orbit Torque switches efficiently a thick ferromagnet too. The current-induced Seeded Spin-Orbit Torque switching mechanism provides a path to the development of highly efficient and thermally stable spintronic devices. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W54.00009: Pattern recognition with neuromorphic computing using magnetic-field induced dynamics of skyrmions Tomoyuki Yokouchi, Satoshi Sugimoto, Bivas Rana, Shinichiro Seki, Naoki Ogawa, Yuki Shiomi, Shinya Kasai, Yoshichika Otani Nonlinear phenomena in physical systems can be used for brain-inspired computing with low energy consumption. Response from the dynamics of a topological spin structure called skyrmion is one of the candidates for such a neuromorphic computing. However, its ability has not been well explored experimentally. Here, we experimentally demonstrate neuromorphic computing using nonlinear response originating from magnetic-field induced dynamics of skyrmions. We designed a simple-structured skyrmion-based neuromorphic device and succeeded in handwritten digit recognition with the accuracy as large as 94.7 % and waveform recognition. Notably, there exists a positive correlation between the recognition accuracy and the number of skyrmions in the devices. The large degree of freedoms of skyrmion systems, such as the position and the size, originate the more complex nonlinear mapping and the larger output dimension, and thus high accuracy. Our results provide a guideline for developing energy-saving and high-performance skyrmion neuromorphic computing devices. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W54.00010: Topological charge-dependent motion of the emergent magnetic monopole in soft magnetic elements Hee-Sung Han, Sooseok Lee, Gyungchoon Go, Namkyu Kim, Wooyoun Kim, Weilun Chao, Young-Sang Yu, Se Kwon Kim, Ki-Suk Lee, Mi-Young Im The emergent magnetic monopole, called Bloch point, is a zero-dimensional spin texture where the local magnetization vanishes, characterized by the topological charge q = ±1 in a three-dimensional magnet [1-3]. In contrast to 2D topological spin textures such as skyrmion, monopoles show novel physical behaviors. For example, it shows pinning and depinning behavior at the atomic lattice [4] and ultrafast dynamics in cylindrical nanowires [5]. Despite of intriguing physical behaviors of the monopole, the topological charge-dependent behaviors of the monopole have not been addressed yet due to the difficulty of securing the topologically different monopoles in magnetic materials. Here, we will show the topological charge-dependent motion of the monopole in Ni80Fe20 (Permalloy) elements, observed by utilizing magnetic transmission soft x-ray microscopy [6]. By performing complementary micromagnetic simulation, we found that the transverse deflection of the monopole is associated with the pinning and depinning behavior of the monopole at the atomic lattice. We believe that this work simulates further research on the experimental studies of monopoles. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W54.00011: Diagnosing the Non-Abelian Kitaev Quantum Spin Liquid via Modular Commutator Kyusung Hwang, Eun-Gook Moon We argue that a non-abelian quantum spin liquid phase can be probed by numerical calculations of modular commutator. Modular commutator is a new measure of quantum entanglement that is closely related with the chiral central charge [1,2], which determines the boundary energy flow and quantized thermal Hall effect of a non-abelian quantum spin liquid. We compute the modular commutator for the Kitaev’s chiral spin liquid by employing exact diagonalization. Our calculations show that the modular commutator is half-quantized in the phase of Kitaev's chiral spin liquid as expected from the chiral central charge. We point out subtleties with exact diagonalization on a 24-site cluster in connection with topological degeneracy on a torus geometry and discuss how to resolve the subtleties by using symmetries. Our results suggest that the modular commutator is a useful probe for non-abelian quantum spin liquids. |
Thursday, March 9, 2023 5:36PM - 5:48PM |
W54.00012: Prediction of Stimulation Strength of Transcranial Magnetic Stimulation in the Brain with Deep Encoder-Decoder Convolutional Neural Network Mohannad Tashli, Muhammad S Alam, Jiaying Gong, Connor Lewis, Ravi L Hadimani, Carrie L Peterson, Hoda Eldardiry, Jayasimha Atulasimha Transcranial magnetic stimulation (TMS) is a non-invasive, effective, and safe neuromodulation technique to treat neurological and psychiatric disorders. However, it is difficult to precisely assess whether crucial brain areas have received the appropriate degree of generated electric field due to the complexity and variety of the brain's composition and structure. Electric field distribution may be calculated numerically using finite element analysis (FEA). These techniques take a lot of time and require extremely high computing resources. In this study, we created a deep convolutional neural network (DCNN) encoder-decoder model to predict induced electric fields from T1- and T2-weighted MRI-based anatomical slices in real time. To test resting motor thresholds, we gathered 11 healthy subjects and applied TMS on the primary motor cortex. SimNIBS pipeline was used to create head models from the subjects' MRI scans. For each subject, the overall size of the head models was scaled to 20 new size scales, resulting in a total of 231 head models. The quantity of input data representing various head model sizes was scaled up. The induced electric fields were calculated using Sim4Life, a FEA program, and utilized as the DCNN training data. Peak signal to noise ratios for the training and testing sets of data for the trained network were 32.83 dB and 28.01 dB, respectively. Our model's primary contribution is its capability to forecast the induced electric fields in real-time, which enables us to precisely and effectively estimate the required TMS intensity in the targeted brain areas. |
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