1
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Zhou Y, Li S, Liang X, Zhou Y. Topological Spin Textures: Basic Physics and Devices. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024:e2312935. [PMID: 38861696 DOI: 10.1002/adma.202312935] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 05/24/2024] [Indexed: 06/13/2024]
Abstract
In the face of escalating modern data storage demands and the constraints of Moore's Law, exploring spintronic solutions, particularly the devices based on magnetic skyrmions, has emerged as a promising frontier in scientific research. Since the first experimental observation of skyrmions, topological spin textures have been extensively studied for their great potential as efficient information carriers in spintronic devices. However, significant challenges have emerged alongside this progress. This review aims to synthesize recent advances in skyrmion research while addressing the major issues encountered in the field. Additionally, current research on promising topological spin structures in addition to skyrmions is summarized. Beyond 2D structures, exploration also extends to 1D magnetic solitons and 3D spin textures. In addition, a diverse array of emerging magnetic materials is introduced, including antiferromagnets and 2D van der Waals magnets, broadening the scope of potential materials hosting topological spin textures. Through a systematic examination of magnetic principles, topological categorization, and the dynamics of spin textures, a comprehensive overview of experimental and theoretical advances in the research of topological magnetism is provided. Finally, both conventional and unconventional applications are summarized based on spin textures proposed thus far. This review provides an outlook on future development in applied spintronics.
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Affiliation(s)
- Yuqing Zhou
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong, 518172, China
| | - Shuang Li
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong, 518172, China
| | - Xue Liang
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong, 518172, China
| | - Yan Zhou
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong, 518172, China
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2
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Saini S, Bindal N, Raj RK, Kaushik BK. A spin wave driven skyrmion-based diode on a T-shaped nanotrack. NANOSCALE 2024. [PMID: 38623868 DOI: 10.1039/d4nr00482e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/17/2024]
Abstract
The propagation of spin waves is one of the promising ways to design nanoscale spintronic devices. The spin waves can interact with the magnetic skyrmion, a particle-like object that is topologically stabilized by Dzyaloshinskii-Moriya interaction (DMI) in thin film heterostructures. In this work, a spin wave-driven skyrmion-based diode is proposed by employing a T-shaped ferromagnetic nanotrack. The one-way motion of the skyrmion is achieved by exploiting the mid-arm at the center of the nanotrack. This prevents the reverse motion of the skyrmion owing to the skyrmion Hall effect (SkHE) and the absence of a repulsive force from the far edge in the mid-arm region. In order to facilitate the diode functionality of the spin wave-driven skyrmion, the amplitude and frequency of the excitation field should be considered in the ranges 0.07 T ≤ H0 ≤ 0.4 T and 60 GHz ≤ f ≤ 80 GHz, respectively. The micromagnetic interaction energy between the edges and the spin wave-driven skyrmion creates a potential gradient that induces the force which is responsible for the longitudinal motion of the skyrmion. The suggested spin wave driven diode exhibits a processing speed on the order of 100 m s-1 at 60 GHz frequency and 0.4 T amplitude. Hence, this device paves the way for the development of complete non-charge based magnetic devices for various spintronic applications.
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Affiliation(s)
- Shipra Saini
- Department of Electronics and Communication Engineering, Indian Institute of Technology, Roorkee, Uttarakhand, 247667, India.
| | - Namita Bindal
- Department of Electronics and Communication Engineering, Indian Institute of Technology, Roorkee, Uttarakhand, 247667, India.
| | - Ravish Kumar Raj
- Department of Electronics and Communication Engineering, Indian Institute of Technology, Roorkee, Uttarakhand, 247667, India.
| | - Brajesh Kumar Kaushik
- Department of Electronics and Communication Engineering, Indian Institute of Technology, Roorkee, Uttarakhand, 247667, India.
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3
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Zhang X, Xia J, Tretiakov OA, Ezawa M, Zhao G, Zhou Y, Liu X, Mochizuki M. Chiral Skyrmions Interacting with Chiral Flowers. NANO LETTERS 2023; 23:11793-11801. [PMID: 38055779 PMCID: PMC10755743 DOI: 10.1021/acs.nanolett.3c03792] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Revised: 12/02/2023] [Accepted: 12/04/2023] [Indexed: 12/08/2023]
Abstract
The chiral nature of active matter plays an important role in the dynamics of active matter interacting with chiral structures. Skyrmions are chiral objects, and their interactions with chiral nanostructures can lead to intriguing phenomena. Here, we explore the random-walk dynamics of a thermally activated chiral skyrmion interacting with a chiral flower-like obstacle in a ferromagnetic layer, which could create topology-dependent outcomes. It is a spontaneous mesoscopic order-from-disorder phenomenon driven by the thermal fluctuations and topological nature of skyrmions that exists only in ferromagnetic and ferrimagnetic systems. The interactions between the skyrmions and chiral flowers at finite temperatures can be utilized to control the skyrmion position and distribution without applying any external driving force or temperature gradient. The phenomenon that thermally activated skyrmions are dynamically coupled to chiral flowers may provide a new way to design topological sorting devices.
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Affiliation(s)
- Xichao Zhang
- Department
of Applied Physics, Waseda University, Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
| | - Jing Xia
- Department
of Electrical and Computer Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan
| | - Oleg A. Tretiakov
- School
of Physics, The University of New South
Wales, Sydney 2052, Australia
| | - Motohiko Ezawa
- Department
of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-8656, Japan
| | - Guoping Zhao
- College
of Physics and Electronic Engineering, Sichuan
Normal University, Chengdu 610068, China
| | - Yan Zhou
- School
of
Science and Engineering, The Chinese University
of Hong Kong, Shenzhen, Guangdong 518172, China
| | - Xiaoxi Liu
- Department
of Electrical and Computer Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan
| | - Masahito Mochizuki
- Department
of Applied Physics, Waseda University, Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
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4
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Chen R, Chen C, Han L, Liu P, Su R, Zhu W, Zhou Y, Pan F, Song C. Ordered creation and motion of skyrmions with surface acoustic wave. Nat Commun 2023; 14:4427. [PMID: 37481619 PMCID: PMC10363109 DOI: 10.1038/s41467-023-40131-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Accepted: 07/04/2023] [Indexed: 07/24/2023] Open
Abstract
Magnetic skyrmions with a well-defined spin texture have shown unprecedented potential for various spintronic applications owning to their topologically non-trivial and quasiparticle properties. To put skyrmions into practical technology, efficient manipulation, especially the inhibition of skyrmion Hall effect (SkHE) has been intensively pursued. In spite of the recent progress made on reducing SkHE in several substituted systems, such as ferrimagnets and synthetic antiferromagnets, the organized creation and current driven motion of skyrmions with negligible SkHE in ferromagnets remain challenging. Here, by embedding the [Co/Pd] multilayer into a surface acoustic wave (SAW) delay line where the longitudinal leaky SAW is excited to provide both the strain and thermal effect, we experimentally realized the ordered generation of magnetic skyrmions. The resultant current-induced skyrmions movement with negligible SkHE was observed, which can be attributed to the energy redistribution of the system during the excitation of SAW. Our findings open up an unprecedentedly new perspective for manipulating topological solitons, which could possibly trigger the future discoveries in skyrmionics and spin acousto-electronics.
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Affiliation(s)
- Ruyi Chen
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Beijing Innovation Center for Future Chip, Tsinghua University, Beijing, 100084, China
| | - Chong Chen
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Beijing Innovation Center for Future Chip, Tsinghua University, Beijing, 100084, China
| | - Lei Han
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Beijing Innovation Center for Future Chip, Tsinghua University, Beijing, 100084, China
| | - Peisen Liu
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Beijing Innovation Center for Future Chip, Tsinghua University, Beijing, 100084, China
| | - Rongxuan Su
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Beijing Innovation Center for Future Chip, Tsinghua University, Beijing, 100084, China
| | - Wenxuan Zhu
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Beijing Innovation Center for Future Chip, Tsinghua University, Beijing, 100084, China
| | - Yongjian Zhou
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Beijing Innovation Center for Future Chip, Tsinghua University, Beijing, 100084, China
| | - Feng Pan
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Beijing Innovation Center for Future Chip, Tsinghua University, Beijing, 100084, China
| | - Cheng Song
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Beijing Innovation Center for Future Chip, Tsinghua University, Beijing, 100084, China.
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5
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Topology dependence of skyrmion Seebeck and skyrmion Nernst effect. Sci Rep 2022; 12:6801. [PMID: 35473940 PMCID: PMC9042842 DOI: 10.1038/s41598-022-10550-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Accepted: 03/28/2022] [Indexed: 11/08/2022] Open
Abstract
We explore the dynamics of skyrmions with various topological charges induced by a temperature gradient in an ultra-thin insulating magnetic film. Combining atomistic spin simulations and analytical calculations we find a topology-dependent skyrmion Seebeck effect: while skyrmions and antiskyrmions move to the hot regime, a topologically trivial localized spin structure moves to the cold regime. We further reveal the emergence of a skyrmion Nernst effect, i.e. finite, topology-dependent velocities transverse to the direction of the temperature gradient. These findings are in agreement with accompanying simulations of skyrmionic motion induced by monochromatic magnon currents, allowing us to demonstrate that the magnonic spin Seebeck effect is responsible for both, skyrmion Seebeck and Nernst effect. Furthermore we employ scattering theory together with Thiele's equation to identify linear momentum transfer from the magnons to the skyrmion as the dominant contribution and to demonstrate that the direction of motion depends on the topological magnon Hall effect and the topological charge of the skyrmion.
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6
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Feng T, Wang P, Wu D. 金属/铁磁绝缘体异质结中的自旋霍尔磁电阻. CHINESE SCIENCE BULLETIN-CHINESE 2022. [DOI: 10.1360/tb-2022-0186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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7
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Real-space observations of 60-nm skyrmion dynamics in an insulating magnet under low heat flow. Nat Commun 2021; 12:5079. [PMID: 34426575 PMCID: PMC8382761 DOI: 10.1038/s41467-021-25291-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2021] [Accepted: 08/03/2021] [Indexed: 11/25/2022] Open
Abstract
Thermal-current induced electron and spin dynamics in solids –dubbed “caloritronics”– have generated widespread interest in both fundamental physics and spintronics applications. Here, we examine the dynamics of nanometric topological spin textures, skyrmions driven by a temperature gradient ∇T or heat flow, that are evaluated through in-situ real-space observations in an insulating helimagnet Cu2OSeO3. We observe increases of the skyrmion velocity and the Hall angle with increasing ∇T above a critical value of ~ 13 mK/mm, which is two orders of magnitude lower than the ∇T required to drive ferromagnetic domain walls. A comparable magnitude of ∇T is also observed to move the domain walls between a skyrmion domain and the non-topological conical-spin domain from cold to hot regions. Our results demonstrate the efficient manipulation of skyrmions by temperature gradients, a promising step towards energy-efficient “green” spintronics. Skyrmions are a type of topological spin texture that great potential across a wide variety of technological applications. Here, Yu et al. study the thermally driven motion of Skyrmions and find a minimum temperature gradient for the motion of skyrmions two orders of magnitude smaller than for domain walls.
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8
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Wang Z, Yuan HY, Cao Y, Li ZX, Duine RA, Yan P. Magnonic Frequency Comb through Nonlinear Magnon-Skyrmion Scattering. PHYSICAL REVIEW LETTERS 2021; 127:037202. [PMID: 34328762 DOI: 10.1103/physrevlett.127.037202] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Accepted: 06/22/2021] [Indexed: 06/13/2023]
Abstract
An optical frequency comb consists of a set of discrete and equally spaced frequencies and has found wide applications in the synthesis over a broad range of spectral frequencies of electromagnetic waves and precise optical frequency metrology. Despite the analogies between magnons and photons in many aspects, the analog of an optical frequency comb in magnonic systems has not been reported. Here, we theoretically study the magnon-skyrmion interaction and find that a magnonic frequency comb (MFC) can be generated above a threshold driving amplitude, where the nonlinear scattering process involving three magnons prevails. The mode spacing of the MFC is equal to the breathing-mode frequency of the skyrmion and is thus tunable by either electric or magnetic means. The theoretical prediction is verified by micromagnetic simulations, and the essential physics can be generalized to a large class of magnetic solitons. Our findings open a new pathway to observe frequency comb structures in magnonic devices that may inspire the study of fundamental nonlinear physics in spintronic platforms in the future.
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Affiliation(s)
- Zhenyu Wang
- School of Electronic Science and Engineering and State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
| | - H Y Yuan
- Institute for Theoretical Physics, Utrecht University, 3584 CC Utrecht, Netherlands
| | - Yunshan Cao
- School of Electronic Science and Engineering and State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
| | - Z-X Li
- School of Electronic Science and Engineering and State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
| | - Rembert A Duine
- Institute for Theoretical Physics, Utrecht University, 3584 CC Utrecht, Netherlands
| | - Peng Yan
- School of Electronic Science and Engineering and State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
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9
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Teixeira AW, Castillo-Sepúlveda S, Rizzi LG, Nunez AS, Troncoso RE, Altbir D, Fonseca JM, Carvalho-Santos VL. Motion-induced inertial effects and topological phase transitions in skyrmion transport. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:265403. [PMID: 33902016 DOI: 10.1088/1361-648x/abfb8c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Accepted: 04/26/2021] [Indexed: 06/12/2023]
Abstract
When the skyrmion dynamics beyond the particle-like description is considered, this topological structure can deform due to a self-induced field. In this work, we perform Monte Carlo simulations to characterize the skyrmion deformation during its steady movement. In the low-velocity regime, the deformation in the skyrmion shape is quantified by an effective inertial mass, which is related to the dissipative force. When skyrmions move faster, the large self-induced deformation triggers topological transitions. These transitions are characterized by the proliferation of skyrmions and a different total topological charge, which is obtained as a function of the skyrmion velocity. Our findings provide an alternative way to describe the dynamics of a skyrmion that accounts for the deformations of its structure. Furthermore, such motion-induced topological phase transitions make it possible to control the number of ferromagnetic skyrmions through velocity effects.
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Affiliation(s)
- A W Teixeira
- Departamento de Física, Universidade Federal de Viçosa, 36570-900, Viçosa, Brazil
| | - S Castillo-Sepúlveda
- Facultad de Ingeniería, Universidad Autónoma de Chile, Av. Pedro de Valdivia 425, Providencia, Santiago, Chile
| | - L G Rizzi
- Departamento de Física, Universidade Federal de Viçosa, 36570-900, Viçosa, Brazil
| | - A S Nunez
- Departamento de Física, FCFM, CEDENNA, Universidad de Chile, Santiago, Chile
| | - R E Troncoso
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - D Altbir
- Departamento de Física, CEDENNA, Universidad de Santiago de Chile, USACH, Santiago, Chile
| | - J M Fonseca
- Departamento de Física, Universidade Federal de Viçosa, 36570-900, Viçosa, Brazil
| | - V L Carvalho-Santos
- Departamento de Física, Universidade Federal de Viçosa, 36570-900, Viçosa, Brazil
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10
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Eilmsteiner D, Wang XG, Chotorlishvili L, Paischer S, Hoffmann M, Buczek P, Ernst A. Asymmetry in the propagation of vortex domain wall artificial skyrmion composite system. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:185803. [PMID: 33711837 DOI: 10.1088/1361-648x/abee39] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 03/12/2021] [Indexed: 06/12/2023]
Abstract
We studied the propagation of an artificial skyrmion coupled to the vortex domain wall (VDW). We discovered the following effect: depending on the propagation's direction, the dynamics of the coupled skyrmion VDW can be faster than the isolated VDW's velocity. The reason for such behavior is the structural distortion that occurs in the coupled system. We interpret the numerical results in terms of the modified Thiele's equation. In particular, increasing the Thiele's equation counteractive coefficient leads to the perfect fitting with the micromagnetic simulation results.
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Affiliation(s)
- D Eilmsteiner
- Institute for Theoretical Physics, Johannes Kepler University Linz, 4040 Linz, Austria
| | - Xi-Guang Wang
- School of Physics and Electronics, Central South University, Changsha 410083, People's Republic of China
| | - L Chotorlishvili
- Institute für Physik, Martin-Luther Universität Halle-Wittenberg, D-06120 Halle/Saale, Germany
| | - S Paischer
- Institute for Theoretical Physics, Johannes Kepler University Linz, 4040 Linz, Austria
| | - M Hoffmann
- Institute for Theoretical Physics, Johannes Kepler University Linz, 4040 Linz, Austria
| | - P Buczek
- Department of Engineering and Computer Sciences, Hamburg University of Applied Sciences, Berliner Tor 7, 20099 Hamburg, Germany
| | - A Ernst
- Institute for Theoretical Physics, Johannes Kepler University Linz, 4040 Linz, Austria
- Max Planck Institute of Microstructure Physics, 06120 Halle, Germany
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11
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Large positive magnetoresistance and Dzyaloshinskii-Moriya interaction in CrSi driven by Cr 3d localization. Sci Rep 2020; 10:12030. [PMID: 32694707 PMCID: PMC7374744 DOI: 10.1038/s41598-020-67617-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Accepted: 06/03/2020] [Indexed: 11/21/2022] Open
Abstract
Spin chiral systems with Dzyaloshinskii–Moriya (DM) interaction due to broken inversion symmetry are extensively studied for their technological applications in spintronics and thermoelectrics. Here, we report an experimental study on the magnetization, magnetoresistance (MR) and electronic structure of a non-centrosymmetric compound CrSi with B20 crystal structure. Both magnetization and MR shows competing ferromagnetic (FM) and antiferromagnetic (AFM) correlations with the FM correlations being comparatively weaker indicating the presence of DM interaction in CrSi. A large positive MR\documentclass[12pt]{minimal}
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\begin{document}$$\sim \,25\%$$\end{document}∼25% obtained at 5 K and 5 T magnetic field arises due to the stronger AFM correlations. Resonant photoemission shows both localized and itinerant nature of Cr 3d electrons to be present in CrSi and this is supported by the temperature dependence of magnetic susceptibility. Drastic variation in the density of states along with valence band broadening at low temperature indicates the increase in hybridization between Cr 3d and Si 3s–3p states which enhances the localization effects. Spin polarized itinerant Cr 3d electrons give rise to AFM spin density wave in CrSi. Magnetic interaction between the localized and itinerant Cr 3d electrons are found to be crucial for realizing DM interaction in this system. Spectral density of states derived from high resolution valence band measurements provides evidence of electronic topological transition in CrSi. Large density of polarized itinerant electrons which varies with temperature and the large positive MR with AFM correlations suggests CrSi as a potential candidate for both the thermoelectric and spintronics applications.
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12
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Chen R, Gao Y, Zhang X, Zhang R, Yin S, Chen X, Zhou X, Zhou Y, Xia J, Zhou Y, Wang S, Pan F, Zhang Y, Song C. Realization of Isolated and High-Density Skyrmions at Room Temperature in Uncompensated Synthetic Antiferromagnets. NANO LETTERS 2020; 20:3299-3305. [PMID: 32282217 DOI: 10.1021/acs.nanolett.0c00116] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Magnetic skyrmions are vortex-like spin textures with nontrivial spin topology and novel physical properties that show promise as an essential building block for novel spintronic applications. Skyrmions in synthetic antiferromagnets (SAF) have been proposed long-term to have many advantages than those in ferromagnetic materials, which suffer from fundamental limits for size and efficient manipulation. Thus, experimental realization of skyrmions in SAF is intensely pursued. Here we show the observation of zero-field stable magnetic skyrmions at room temperature in SAF [Co/Pd]/Ru/[Co/Pd] multilayers with Lorentz transmission electron microscope, where uncompensated moments of the SAF provide a medium for the skyrmion characterization. Isolated skyrmions and high-density skyrmions via magnetic field and electromagnetic coordinated methods have been observed, respectively. These created high-density skyrmions maintain at zero-field even when both the current and magnetic field are removed. The use of skyrmions in SAF would advance the process toward practical nonvolatile memories based on spin topology.
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Affiliation(s)
- Ruyi Chen
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
| | - Yang Gao
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Institute of Advanced Materials, Beijing Normal University, Beijing 100875, China
| | - Xichao Zhang
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong 518172, China
| | - Ruiqi Zhang
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
| | - Siqi Yin
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
| | - Xianzhe Chen
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
| | - Xiaofeng Zhou
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
| | - Yongjian Zhou
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
| | - Jing Xia
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong 518172, China
| | - Yan Zhou
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong 518172, China
| | - Shouguo Wang
- Institute of Advanced Materials, Beijing Normal University, Beijing 100875, China
| | - Feng Pan
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
| | - Ying Zhang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Cheng Song
- Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
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13
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Zhang X, Zhou Y, Mee Song K, Park TE, Xia J, Ezawa M, Liu X, Zhao W, Zhao G, Woo S. Skyrmion-electronics: writing, deleting, reading and processing magnetic skyrmions toward spintronic applications. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:143001. [PMID: 31689688 DOI: 10.1088/1361-648x/ab5488] [Citation(s) in RCA: 59] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The field of magnetic skyrmions has been actively investigated across a wide range of topics during the last decades. In this topical review, we mainly review and discuss key results and findings in skyrmion research since the first experimental observation of magnetic skyrmions in 2009. We particularly focus on the theoretical, computational and experimental findings and advances that are directly relevant to the spintronic applications based on magnetic skyrmions, i.e. their writing, deleting, reading and processing driven by magnetic field, electric current and thermal energy. We then review several potential applications including information storage, logic computing gates and non-conventional devices such as neuromorphic computing devices. Finally, we discuss possible future research directions on magnetic skyrmions, which also cover rich topics on other topological textures such as antiskyrmions and bimerons in antiferromagnets and frustrated magnets.
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Affiliation(s)
- Xichao Zhang
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong 518172, People's Republic of China
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14
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Kim BS. Skyrmions and Hall transport. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:383001. [PMID: 31167174 DOI: 10.1088/1361-648x/ab273f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We review recent progresses towards an understanding of the skyrmion Hall transport in insulating as well as conducting materials. First, we consider a theoretical breakthrough based on the quantum field theory ward identity, a first principle analysis, relying on symmetries and conservation laws. Broken parity (inversion) symmetry plays a crucial role in skyrmion Hall transport. In addition to the well known thermal and electric Hall conductivities, our analysis has led us to the discovery of a new and unforeseen physical quantity, Hall viscosity-an anti-symmetric part of the viscosity tensor. We propose a simple way to confirm the existence of Hall viscosity in the measurements of Hall conductivity as a function of momentum. We provide various background materials to assist the readers to understand the quantum field theory ward identity. In the second part, we review recent theoretical and experimental advancements of the skyrmion Hall effects and the topological (magnon) Hall effects for conducting (insulting) magnets. For this purpose, we consider two enveloping themes: spin torque and thermo-electromagnetic effect. First, we overview various spin torques, such as spin transfer torque, spin-orbit torque, and spin Hall torque, and generalized Landau-Lifshitz-Gilbert equations and Thiele equations using a phenomenological approach. Second, we consider irreversible thermodynamics to survey possible thermo-electromagnetic effects, such as Seebeck, Peltier and Thompson effects in the presence of the electric currents, along with the Hall effects in the presence of a background magnetic field. Recently developed spin Seebeck effects are also a significant part of the survey. We also accommodate extensive background materials to make this review self-contained. Finally, we revisit the skyrmion Hall transport from the ward identity view point.
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Affiliation(s)
- Bom Soo Kim
- Department of Physics, Loyola University Maryland, 4501 N. Charles Street, Baltimore, MD 21210, United States of America
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15
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Affiliation(s)
- Yan Zhou
- School of Science and Engineering, The Chinese University of Hong Kong, China
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16
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Psaroudaki C, Loss D. Skyrmions Driven by Intrinsic Magnons. PHYSICAL REVIEW LETTERS 2018; 120:237203. [PMID: 29932693 DOI: 10.1103/physrevlett.120.237203] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2018] [Indexed: 05/10/2023]
Abstract
We study the dynamics of a Skyrmion in a magnetic insulating nanowire in the presence of time-dependent oscillating magnetic field gradients. These ac fields act as a net driving force on the Skyrmion via its own intrinsic magnetic excitations. In a microscopic quantum field theory approach, we include the unavoidable coupling of the external field to the magnons, which gives rise to time-dependent dissipation for the Skyrmion. We demonstrate that the magnetic ac field induces a super-Ohmic to Ohmic crossover behavior for the Skyrmion dissipation kernels with time-dependent Ohmic terms. The ac driving of the magnon bath at resonance results in a unidirectional helical propagation of the Skyrmion in addition to the otherwise periodic bounded motion.
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Affiliation(s)
- Christina Psaroudaki
- Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
| | - Daniel Loss
- Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
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17
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Yang W, Yang H, Cao Y, Yan P. Photonic orbital angular momentum transfer and magnetic skyrmion rotation. OPTICS EXPRESS 2018; 26:8778-8790. [PMID: 29715841 DOI: 10.1364/oe.26.008778] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Accepted: 03/19/2018] [Indexed: 06/08/2023]
Abstract
Magnetic skyrmions are chiral quasiparticles that show promise for future spintronic applications such as skyrmion racetrack memories and logic devices because of their topological stability, small size (typically ∼ 3 - 500 nm), and ultralow threshold force to drive their motion. On the other hand, the ability of light to carry and deliver orbital angular momentum (OAM) in the form of optical vortices has attracted a lot of interest. In this work, we predict a photonic OAM transfer effect, by studying the dynamics of magnetic skyrmions subject to Laguerre-Gaussian optical vortices, which manifests a rotational motion of the skyrmionic quasiparticle around the beam axis. The topological charge of the optical vortex determines both the magnitude and the handedness of the rotation velocity of skyrmions. In our proposal, the twisted light beam acts as an optical tweezer to enable us displacing skyrmions over large-scale defects in magnetic films to avoid being captured.
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18
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Chen X, Kang W, Zhu D, Zhang X, Lei N, Zhang Y, Zhou Y, Zhao W. A compact skyrmionic leaky-integrate-fire spiking neuron device. NANOSCALE 2018; 10:6139-6146. [PMID: 29557440 DOI: 10.1039/c7nr09722k] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Neuromorphic computing, which relies on a combination of a large number of neurons massively interconnected by an even larger number of synapses, has been actively studied for its characteristics such as energy efficiency, intelligence, and adaptability. To date, while the development of artificial synapses has shown great progress with the introduction of emerging nanoelectronic devices, e.g., memristive devices, the implementation of artificial neurons, however, depends mostly on semiconductor-based circuits via integrating many transistors, sacrificing energy efficiency and integration density. Here, we present a novel compact neuron device that exploits the current-driven magnetic skyrmion dynamics in a wedge-shaped nanotrack. Under the coaction of the exciting current pulse and the repulsive force exerted by the nanotrack edges, the dynamic behavior of the proposed skyrmionic artificial neuron device is in analogy to the leaky-integrate-fire (LIF) spiking function of a biological neuron. The tunable temporary location of the skyrmion in our artificial neuron behaves like the analog membrane potential of a biological neuron. The neuronal dynamics and the related physical interpretations of the proposed skyrmionic neuron device are carefully investigated via micromagnetic and theoretical methods. Such a compact artificial neuron enables energy-efficient and high-density implementation of neuromorphic computing hardware.
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Affiliation(s)
- Xing Chen
- Fert Beijing Institute, BDBC, and School of Electronic and Information Engineering, Beihang University, Beijing 100191, China.
| | - Wang Kang
- Fert Beijing Institute, BDBC, and School of Electronic and Information Engineering, Beihang University, Beijing 100191, China.
| | - Daoqian Zhu
- Fert Beijing Institute, BDBC, and School of Electronic and Information Engineering, Beihang University, Beijing 100191, China.
| | - Xichao Zhang
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, 518172, China
| | - Na Lei
- Fert Beijing Institute, BDBC, and School of Electronic and Information Engineering, Beihang University, Beijing 100191, China.
| | - Youguang Zhang
- Fert Beijing Institute, BDBC, and School of Electronic and Information Engineering, Beihang University, Beijing 100191, China.
| | - Yan Zhou
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, 518172, China
| | - Weisheng Zhao
- Fert Beijing Institute, BDBC, and School of Electronic and Information Engineering, Beihang University, Beijing 100191, China.
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19
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Abstract
The photon-assisted magnetic recording utilizes the ultrafast laser to excite the spin wave in the magnetic nanostructures and accordingly switch its magnetization state. Here, by means of micromagnetic simulation, the motion of magnetic skyrmions, a topologically protected chiral magnet with few nanometer size, induced by the spin wave is studied. It is found that the magnetic skyrmion can move in the same direction of spin-wave propagation, which is first accelerated and then decelerated exponentially. The magnetic skyrmion motion originated from the robust coupling of the spin waves with the skyrmion, through the SW’s linear momentum transfer torque acting on the skyrmion. Besides amplitude, the reflectivity of the spin wave by skyrmion has tremendous impact on the velocity of skyrmion motion. The skyrmion velocities are mainly determined by the reflectivity, when the spin-wave amplitude is almost identical. Our results give guidance for the design and development of spin-wave control spintronics.
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20
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Kharkov YA, Sushkov OP, Mostovoy M. Bound States of Skyrmions and Merons near the Lifshitz Point. PHYSICAL REVIEW LETTERS 2017; 119:207201. [PMID: 29219354 DOI: 10.1103/physrevlett.119.207201] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Indexed: 06/07/2023]
Abstract
We study topological defects in anisotropic ferromagnets with competing interactions near the Lifshitz point. We show that Skyrmions and bimerons are stable in a large part of the phase diagram. We calculate Skyrmion-Skyrmion and meron-meron interactions and show that Skyrmions attract each other and form ring-shaped bound states in a zero magnetic field. At the Lifshitz point merons carrying a fractional topological charge become deconfined. These results imply that unusual topological excitations may exist in weakly frustrated magnets with conventional crystal lattices.
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Affiliation(s)
- Y A Kharkov
- School of Physics, University of New South Wales, Sydney 2052, Australia
| | - O P Sushkov
- School of Physics, University of New South Wales, Sydney 2052, Australia
| | - M Mostovoy
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, Netherlands
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21
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Müller J, Rajeswari J, Huang P, Murooka Y, Rønnow HM, Carbone F, Rosch A. Magnetic Skyrmions and Skyrmion Clusters in the Helical Phase of Cu_{2}OSeO_{3}. PHYSICAL REVIEW LETTERS 2017; 119:137201. [PMID: 29341720 DOI: 10.1103/physrevlett.119.137201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Indexed: 06/07/2023]
Abstract
Skyrmions are nanometric spin whirls that can be stabilized in magnets lacking inversion symmetry. The properties of isolated Skyrmions embedded in a ferromagnetic background have been intensively studied. We show that single Skyrmions and clusters of Skyrmions can also form in the helical phase and investigate theoretically their energetics and dynamics. The helical background provides natural one-dimensional channels along which a Skyrmion can move rapidly. In contrast to Skyrmions in ferromagnets, the Skyrmion-Skyrmion interaction has a strong attractive component and thus Skyrmions tend to form clusters with characteristic shapes. These clusters are directly observed in transmission electron microscopy measurements in thin films of Cu_{2}OSeO_{3}. Topological quantization, high mobility, and the confinement of Skyrmions in channels provided by the helical background may be useful for future spintronics devices.
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Affiliation(s)
- Jan Müller
- Institute for Theoretical Physics, University of Cologne, D-50937 Cologne, Germany
| | - Jayaraman Rajeswari
- Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), Institute of Physics, EPFL, CH-1015 Lausanne, Switzerland
| | - Ping Huang
- Laboratory for Quantum Magnetism (LQM), Institute of Physics, EPFL, CH-1015 Lausanne, Switzerland
| | - Yoshie Murooka
- Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), Institute of Physics, EPFL, CH-1015 Lausanne, Switzerland
| | - Henrik M Rønnow
- Laboratory for Quantum Magnetism (LQM), Institute of Physics, EPFL, CH-1015 Lausanne, Switzerland
| | - Fabrizio Carbone
- Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), Institute of Physics, EPFL, CH-1015 Lausanne, Switzerland
| | - Achim Rosch
- Institute for Theoretical Physics, University of Cologne, D-50937 Cologne, Germany
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22
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Kanazawa N, Seki S, Tokura Y. Noncentrosymmetric Magnets Hosting Magnetic Skyrmions. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2017; 29:1603227. [PMID: 28306166 DOI: 10.1002/adma.201603227] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Revised: 11/30/2016] [Indexed: 06/06/2023]
Abstract
The concept of a skyrmion, which was first introduced by Tony Skyrme in the field of particle physics, has become widespread in condensed matter physics to describe various topological orders. Skyrmions in magnetic materials have recently received particular attention; they represent vortex-like spin structures with the character of nanometric particles and produce fascinating physical properties rooted in their topological nature. Here, a series of noncentrosymmetric ferromagnets hosting skyrmions is reviewed: B20 metals, Cu2 OSeO3 , Co-Zn-Mn alloys, and GaV4 S8 , where Dzyaloshinskii-Moriya interaction plays a key role in the stabilization of skyrmion spin texture. Their topological spin arrangements and consequent emergent electromagnetic fields give rise to striking features in transport and magnetoelectric properties in metals and insulators, such as the topological Hall effect, efficient electric-drive of skyrmions, and multiferroic behavior. Such electric controllability and nanometric particle natures highlight magnetic skyrmions as a potential information carrier for high-density magnetic storage devices with excellent energy efficiency.
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Affiliation(s)
- Naoya Kanazawa
- Department of Applied Physics, University of Tokyo, Tokyo, 113-8656, Japan
| | - Shinichiro Seki
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
| | - Yoshinori Tokura
- Department of Applied Physics, University of Tokyo, Tokyo, 113-8656, Japan
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
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23
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Díaz SA, Troncoso RE. Controlling skyrmion helicity via engineered Dzyaloshinskii-Moriya interactions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:426005. [PMID: 27588612 DOI: 10.1088/0953-8984/28/42/426005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Single magnetic skyrmion dynamics in chiral magnets with a spatially inhomogeneous Dzyaloshinskii-Moriya interaction (DMI) is considered. Based on the relation between DMI coupling and skyrmion helicity, it is argued that the latter must be included as an extra degree of freedom in the dynamics of skyrmions. An effective description of the skyrmion dynamics for an arbitrary inhomogeneous DMI coupling is obtained through the collective coordinates method. The resulting generalized Thiele equation is a dynamical system for the center of mass position and helicity of the skyrmion. It is found that the dissipative tensor and hence the Hall angle become helicity dependent. The skyrmion position and helicity dynamics are fully characterized by our model in two particular examples of engineered DMI coupling: half-planes with opposite-sign DMI and linearly varying DMI. In light of the experiment of Shibata et al (2013 Nat. Nanotechnol. 8 723) on the magnitude and sign of the DMI, our results constitute the first step toward a more complete understanding of the skyrmion helicity as a new degree of freedom that could be harnessed in future high-density magnetic storage and logic devices.
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Affiliation(s)
- Sebastián A Díaz
- Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA
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24
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Zhang SL, Bauer A, Burn DM, Milde P, Neuber E, Eng LM, Berger H, Pfleiderer C, van der Laan G, Hesjedal T. Multidomain Skyrmion Lattice State in Cu2OSeO3. NANO LETTERS 2016; 16:3285-3291. [PMID: 27070961 DOI: 10.1021/acs.nanolett.6b00845] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Magnetic skyrmions in chiral magnets are nanoscale, topologically protected magnetization swirls that are promising candidates for spintronics memory carriers. Therefore, observing and manipulating the skyrmion state on the surface level of the materials are of great importance for future applications. Here, we report a controlled way of creating a multidomain skyrmion state near the surface of a Cu2OSeO3 single crystal, observed by soft resonant elastic X-ray scattering. This technique is an ideal tool to probe the magnetic order at the L3 edge of 3d metal compounds giving an average depth sensitivity of ∼50 nm. The single-domain 6-fold-symmetric skyrmion lattice can be broken up into domains, overcoming the propagation directions imposed by the cubic anisotropy by applying the magnetic field in directions deviating from the major cubic axes. Our findings open the door to a new way to manipulate and engineer the skyrmion state locally on the surface or on the level of individual skyrmions, which will enable applications in the future.
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Affiliation(s)
- S L Zhang
- Clarendon Laboratory, Department of Physics, University of Oxford , Parks Road, Oxford OX1 3PU, United Kingdom
| | - A Bauer
- Physik Department, Technische Universität München , 85748 Garching, Germany
| | - D M Burn
- Diamond Light Source , Didcot OX11 0DE, United Kingdom
| | - P Milde
- Institut für Angewandte Photophysik, TU Dresden , 01069 Dresden, Germany
| | - E Neuber
- Institut für Angewandte Photophysik, TU Dresden , 01069 Dresden, Germany
| | - L M Eng
- Institut für Angewandte Photophysik, TU Dresden , 01069 Dresden, Germany
| | - H Berger
- Crystal Growth Facility, Ecole Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland
| | - C Pfleiderer
- Physik Department, Technische Universität München , 85748 Garching, Germany
| | - G van der Laan
- Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE, United Kingdom
| | - T Hesjedal
- Clarendon Laboratory, Department of Physics, University of Oxford , Parks Road, Oxford OX1 3PU, United Kingdom
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25
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Magnetic bilayer-skyrmions without skyrmion Hall effect. Nat Commun 2016; 7:10293. [PMID: 26782905 PMCID: PMC4735649 DOI: 10.1038/ncomms10293] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 11/26/2015] [Indexed: 11/12/2022] Open
Abstract
Magnetic skyrmions might be used as information carriers in future advanced memories, logic gates and computing devices. However, there exists an obstacle known as the skyrmion Hall effect (SkHE), that is, the skyrmion trajectories bend away from the driving current direction due to the Magnus force. Consequently, the skyrmions in constricted geometries may be destroyed by touching the sample edges. Here we theoretically propose that the SkHE can be suppressed in the antiferromagnetically exchange-coupled bilayer system, since the Magnus forces in the top and bottom layers are exactly cancelled. We show that such a pair of SkHE-free magnetic skyrmions can be nucleated and be driven by the current-induced torque. Our proposal provides a promising means to move magnetic skyrmions in a perfectly straight trajectory in ultra-dense devices with ultra-fast processing speed. Magnetic skyrmions propagating under an applied current along a nanowire experience the magnus force, deflecting them towards the edges where they may be destroyed, potentially hindering their applications. Here, the authors propose a method to surpass this issue utilizing magnetic bilayers systems.
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26
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Mochizuki M, Seki S. Dynamical magnetoelectric phenomena of multiferroic skyrmions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:503001. [PMID: 26624202 DOI: 10.1088/0953-8984/27/50/503001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Magnetic skyrmions, vortex-like swirling spin textures characterized by a quantized topological invariant, realized in chiral-lattice magnets are currently attracting intense research interest. In particular, their dynamics under external fields is an issue of vital importance both for fundamental science and for technical application. Whereas observations of magnetic skyrmions has been limited to metallic magnets so far, their realization was also discovered in a chiral-lattice insulating magnet Cu2OSeO3 in 2012. Skyrmions in the insulator turned out to exhibit multiferroic nature with spin-induced ferroelectricity. Strong magnetoelectric coupling between noncollinear skyrmion spins and electric polarizations mediated by relativistic spin-orbit interaction enables us to drive motion and oscillation of magnetic skyrmions by application of electric fields instead of injection of electric currents. Insulating materials also provide an environment suitable for detection of pure spin dynamics through spectroscopic measurements owing to the absence of appreciable charge excitations. In this article, we review recent theoretical and experimental studies on multiferroic properties and dynamical magnetoelectric phenomena of magnetic skyrmions in insulators. We argue that multiferroic skyrmions show unique coupled oscillation modes of magnetizations and polarizations, so-called electromagnon excitations, which are both magnetically and electrically active, and interference between the electric and magnetic activation processes leads to peculiar magnetoelectric effects in a microwave frequency regime.
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Affiliation(s)
- Masahito Mochizuki
- Department of Physics and Mathematics, Aoyama Gakuin University, Kanagawa 252-5258, Japan. PRESTO, Japan Science and Technology Agency (JST), Tokyo 102-0075, Japan
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27
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Hagemeister J, Romming N, von Bergmann K, Vedmedenko EY, Wiesendanger R. Stability of single skyrmionic bits. Nat Commun 2015; 6:8455. [PMID: 26465211 PMCID: PMC4634135 DOI: 10.1038/ncomms9455] [Citation(s) in RCA: 112] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Accepted: 08/21/2015] [Indexed: 11/09/2022] Open
Abstract
The switching between topologically distinct skyrmionic and ferromagnetic states has been proposed as a bit operation for information storage. While long lifetimes of the bits are required for data storage devices, the lifetimes of skyrmions have not been addressed so far. Here we show by means of atomistic Monte Carlo simulations that the field-dependent mean lifetimes of the skyrmionic and ferromagnetic states have a high asymmetry with respect to the critical magnetic field, at which these lifetimes are identical. According to our calculations, the main reason for the enhanced stability of skyrmions is a different field dependence of skyrmionic and ferromagnetic activation energies and a lower attempt frequency of skyrmions rather than the height of energy barriers. We use this knowledge to propose a procedure for the determination of effective material parameters and the quantification of the Monte Carlo timescale from the comparison of theoretical and experimental data. Magnetic skyrmions are swirling magnetization textures which are topologically stabilized in helical magnets under an applied magnetic field. Here, the authors use Monte Carlo simulations to explore the stability of skyrmions against a ferromagnetic phase and their potential as single bits.
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Affiliation(s)
- J Hagemeister
- Department of Physics, Institute of Applied Physics and Interdisciplinary Nanoscience Center Hamburg, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany
| | - N Romming
- Department of Physics, Institute of Applied Physics and Interdisciplinary Nanoscience Center Hamburg, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany
| | - K von Bergmann
- Department of Physics, Institute of Applied Physics and Interdisciplinary Nanoscience Center Hamburg, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany
| | - E Y Vedmedenko
- Department of Physics, Institute of Applied Physics and Interdisciplinary Nanoscience Center Hamburg, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany
| | - R Wiesendanger
- Department of Physics, Institute of Applied Physics and Interdisciplinary Nanoscience Center Hamburg, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany
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28
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Abstract
A linear array of periodically spaced and individually controllable skyrmions is introduced as a magnonic crystal. It is numerically demonstrated that skyrmion nucleation and annihilation can be accurately controlled by a nanosecond spin polarized current pulse through a nanocontact. Arranged in a periodic array, such nanocontacts allow the creation of a skyrmion lattice that causes a periodic modulation of the waveguide's magnetization, which can be dynamically controlled by changing either the strength of an applied external magnetic field or the density of the injected spin current through the nanocontacts. The skyrmion diameter is highly dependent on both the applied field and the injected current. This implies tunability of the lowest band gap as the skyrmion diameter directly affects the strength of the pinning potential. The calculated magnonic spectra thus exhibit tunable allowed frequency bands and forbidden frequency bandgaps analogous to that of conventional magnonic crystals where, in contrast, the periodicity is structurally induced and static. In the dynamic magnetic crystal studied here, it is possible to dynamically turn on and off the artificial periodic structure, which allows switching between full rejection and full transmission of spin waves in the waveguide. These findings should stimulate further research activities on multiple functionalities offered by magnonic crystals based on periodic skyrmion lattices.
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Affiliation(s)
- Fusheng Ma
- †Temasek Laboratories, National University of Singapore, 119077 Singapore
| | - Yan Zhou
- ‡Department of Physics, University of Hong Kong, Hong Kong, P. R. China
- ⊥York-Nanjing Joint Center for Spintronics and Nano Engineering (YNJC), School of Electronics Science and Engineering, Nanjing University, Nanjing 210093, China
| | - H B Braun
- §School of Physics, University College Dublin, Dublin 4, Ireland
| | - W S Lew
- ∥School of Physical and Mathematical Sciences, Nanyang Technological University, 639798 Singapore
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29
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Zhang X, Ezawa M, Xiao D, Zhao GP, Liu Y, Zhou Y. All-magnetic control of skyrmions in nanowires by a spin wave. NANOTECHNOLOGY 2015; 26:225701. [PMID: 25965121 DOI: 10.1088/0957-4484/26/22/225701] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Magnetic skyrmions are topologically protected nanoscale objects, which are promising building blocks for novel magnetic and spintronic devices. Here, we investigate the dynamics of a skyrmion driven by a spin wave in a magnetic nanowire. It is found that (i) the skyrmion is first accelerated and then decelerated exponentially; (ii) it can turn L-corners with both right and left turns; and (iii) it always turns left (right) when the skyrmion number is positive (negative) in the T- and Y-junctions. Our results will be the basis of skyrmionic devices driven by a spin wave.
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Affiliation(s)
- Xichao Zhang
- Department of Physics, The University of Hong Kong, Hong Kong, People's Republic of China
| | - Motohiko Ezawa
- Department of Applied Physics, University of Tokyo, Hongo 7-3-1, 113-8656, Japan
| | - Dun Xiao
- Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physical Science and Engineering, Tongji University, Shanghai 200092, People's Republic of China
| | - G P Zhao
- College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610068, People's Republic of China
- Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Material Technology & Engineering, Chinese Academy of Sciences, Ningbo 315201, People's Republic of China
| | - Yaowen Liu
- Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physical Science and Engineering, Tongji University, Shanghai 200092, People's Republic of China
| | - Yan Zhou
- Department of Physics, The University of Hong Kong, Hong Kong, People's Republic of China
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30
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Dai Y, Wang H, Yang T, Ren W, Zhang Z. Flower-like dynamics of coupled Skyrmions with dual resonant modes by a single-frequency microwave magnetic field. Sci Rep 2014; 4:6153. [PMID: 25141993 PMCID: PMC4139943 DOI: 10.1038/srep06153] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Accepted: 08/04/2014] [Indexed: 11/23/2022] Open
Abstract
Resonant excitations of confined systems have aroused much attention because of their potential application in future microwave devices and spintronics. Under resonant excitations, the motion of topo-logical objects exhibits circular, elliptical or even stadium-like dynamics. However, more complex non-linear resonant excitations of topological objects in confined systems have seldom been reported and the associated physical mechanism remains unclear. Here, we present an observation of flower-like resonant excitations for coupled skyrmions in Co/Ru/Co nanodisks activated by a single-frequency microwave magnetic field by means of numerical simulation. We find that flower-like dynamics of coupled skyrmions is always accompanied by an excitation of an eigenfrequency near 1.15 GHz, which is strongly associated with the large non-local deformation of the topological density distribution of coupled skyrmions. These results distinguish a skyrmion from other topological objects in dynamics and will be instrumental to the manipulation of skyrmions for applications.
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Affiliation(s)
- Yingying Dai
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang, 110016, P. R. China
| | - Han Wang
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang, 110016, P. R. China
| | - Teng Yang
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang, 110016, P. R. China
| | - Weijun Ren
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang, 110016, P. R. China
| | - Zhidong Zhang
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang, 110016, P. R. China
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