1
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Ukleev V, Ajejas F, Devishvili A, Vorobiev A, Steinke NJ, Cubitt R, Luo C, Abrudan RM, Radu F, Cros V, Reyren N, White JS. Observation by SANS and PNR of pure Néel-type domain wall profiles and skyrmion suppression below room temperature in magnetic [Pt/CoFeB/Ru] 10 multilayers. SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 2024; 25:2315015. [PMID: 38455384 PMCID: PMC10919321 DOI: 10.1080/14686996.2024.2315015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Accepted: 01/29/2024] [Indexed: 03/09/2024]
Abstract
We report investigations of the magnetic textures in periodic multilayers [Pt(1 nm)/(CoFeB(0.8 nm)/Ru(1.4 nm)]10 using polarised neutron reflectometry (PNR) and small-angle neutron scattering (SANS). The multilayers are known to host skyrmions stabilized by Dzyaloshinskii-Moriya interactions induced by broken inversion symmetry and spin-orbit coupling at the asymmetric interfaces. From depth-dependent PNR measurements, we observed well-defined structural features and obtained the layer-resolved magnetization profiles. The in-plane magnetization of the CoFeB layers calculated from fitting of the PNR profiles is found to be in excellent agreement with magnetometry data. Using SANS as a bulk probe of the entire multilayer, we observe long-period magnetic stripe domains and skyrmion ensembles with full orientational disorder at room temperature. No sign of skyrmions is found below 250 K, which we suggest is due to an increase of an effective magnetic anisotropy in the CoFeB layer on cooling that suppresses skyrmion stability. Using polarised SANS at room temperature, we prove the existence of pure Néel-type windings in both stripe domain and skyrmion regimes. No Bloch-type winding admixture, i.e. an indication for hybrid windings, is detected within the measurement sensitivity, in good agreement with expectations according to our micromagnetic modelling of the multilayers. Our findings using neutron techniques provide valuable microscopic insights into the rich magnetic behavior of skyrmion-hosting multilayers, which are essential for the advancement of future skyrmion-based spintronic devices.
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Affiliation(s)
- Victor Ukleev
- Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institute (PSI), Villigen, Switzerland
- Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany
| | - Fernando Ajejas
- Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, Palaiseau, France
| | | | - Alexei Vorobiev
- Institut Laue-Langevin, Grenoble, France
- Department of Physics, Uppsala University, Uppsala, Sweden
| | | | | | - Chen Luo
- Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany
| | | | - Florin Radu
- Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany
| | - Vincent Cros
- Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, Palaiseau, France
| | - Nicolas Reyren
- Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, Palaiseau, France
| | - Jonathan S. White
- Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institute (PSI), Villigen, Switzerland
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2
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Singh D, Fujishiro Y, Hayami S, Moody SH, Nomoto T, Baral PR, Ukleev V, Cubitt R, Steinke NJ, Gawryluk DJ, Pomjakushina E, Ōnuki Y, Arita R, Tokura Y, Kanazawa N, White JS. Transition between distinct hybrid skyrmion textures through their hexagonal-to-square crystal transformation in a polar magnet. Nat Commun 2023; 14:8050. [PMID: 38052859 DOI: 10.1038/s41467-023-43814-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 11/21/2023] [Indexed: 12/07/2023] Open
Abstract
Magnetic skyrmions, topological vortex-like spin textures, garner significant interest due to their unique properties and potential applications in nanotechnology. While they typically form a hexagonal crystal with distinct internal magnetisation textures known as Bloch- or Néel-type, recent theories suggest the possibility for direct transitions between skyrmion crystals of different lattice structures and internal textures. To date however, experimental evidence for these potentially useful phenomena have remained scarce. Here, we discover the polar tetragonal magnet EuNiGe3 to host two hybrid skyrmion phases, each with distinct internal textures characterised by anisotropic combinations of Bloch- and Néel-type windings. Variation of the magnetic field drives a direct transition between the two phases, with the modification of the hybrid texture concomitant with a hexagonal-to-square skyrmion crystal transformation. We explain these observations with a theory that includes the key ingredients of momentum-resolved Ruderman-Kittel-Kasuya-Yosida and Dzyaloshinskii-Moriya interactions that compete at the observed low symmetry magnetic skyrmion crystal wavevectors. Our findings underscore the potential of polar magnets with rich interaction schemes as promising for discovering new topological magnetic phases.
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Affiliation(s)
- Deepak Singh
- Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institute (PSI), CH-5232, Villigen, Switzerland.
| | - Yukako Fujishiro
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama, 351-0198, Japan
| | - Satoru Hayami
- Graduate School of Science, Hokkaido University, Sapporo, 060-0810, Japan
| | - Samuel H Moody
- Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institute (PSI), CH-5232, Villigen, Switzerland
| | - Takuya Nomoto
- Research Center for Advanced Science and Technology, University of Tokyo, Komaba, Meguro-ku, Tokyo, 153-8904, Japan
| | - Priya R Baral
- Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institute (PSI), CH-5232, Villigen, Switzerland
| | - Victor Ukleev
- Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109, Berlin, Germany
| | - Robert Cubitt
- Institut-Laue-Langevin, 6 rue Jules Horowitz, Grenoble, 38000, France
| | | | - Dariusz J Gawryluk
- Laboratory for Multiscale Materials Experiments (LMX), Paul Scherrer Institut (PSI), CH-5232, Villigen PSI, Switzerland
| | - Ekaterina Pomjakushina
- Laboratory for Multiscale Materials Experiments (LMX), Paul Scherrer Institut (PSI), CH-5232, Villigen PSI, Switzerland
| | - Yoshichika Ōnuki
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama, 351-0198, Japan
| | - Ryotaro Arita
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama, 351-0198, Japan
- Research Center for Advanced Science and Technology, University of Tokyo, Komaba, Meguro-ku, Tokyo, 153-8904, Japan
| | - Yoshinori Tokura
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama, 351-0198, Japan
- Department of Applied Physics, The University of Tokyo, Bunkyo, Tokyo, 113-8656, Japan
| | - Naoya Kanazawa
- Institute of Industrial Science, The University of Tokyo, Meguro-ku, Tokyo, 153-8505, Japan
| | - Jonathan S White
- Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institute (PSI), CH-5232, Villigen, Switzerland.
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3
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Kato YD, Okamura Y, Hirschberger M, Tokura Y, Takahashi Y. Topological magneto-optical effect from skyrmion lattice. Nat Commun 2023; 14:5416. [PMID: 37669971 PMCID: PMC10480175 DOI: 10.1038/s41467-023-41203-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Accepted: 08/23/2023] [Indexed: 09/07/2023] Open
Abstract
The magnetic skyrmion is a spin-swirling topological object characterized by its nontrivial winding number, holding potential for next-generation spintronic devices. While optical readout has become increasingly important towards the high integration and ultrafast operation of those devices, the optical response of skyrmions has remained elusive. Here, we show the magneto-optical Kerr effect (MOKE) induced by the skyrmion formation, i.e., topological MOKE, in Gd2PdSi3. The significantly enhanced optical rotation found in the skyrmion phase demonstrates the emergence of topological MOKE, exemplifying the light-skyrmion interaction arising from the emergent gauge field. This gauge field in momentum space causes a dramatic reconstruction of the electronic band structure, giving rise to magneto-optical activity ranging up to the sub-eV region. The present findings pave a way for photonic technology based on skyrmionics.
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Affiliation(s)
- Yoshihiro D Kato
- Department of Applied Physics and Quantum Phase Electronics Center, University of Tokyo, Tokyo, 113-8656, Japan
| | - Yoshihiro Okamura
- Department of Applied Physics and Quantum Phase Electronics Center, University of Tokyo, Tokyo, 113-8656, Japan.
| | - Max Hirschberger
- Department of Applied Physics and Quantum Phase Electronics Center, University of Tokyo, Tokyo, 113-8656, Japan
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
| | - Yoshinori Tokura
- Department of Applied Physics and Quantum Phase Electronics Center, University of Tokyo, Tokyo, 113-8656, Japan
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
- Tokyo College, University of Tokyo, Tokyo, 113-8656, Japan
| | - Youtarou Takahashi
- Department of Applied Physics and Quantum Phase Electronics Center, University of Tokyo, Tokyo, 113-8656, Japan.
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan.
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4
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Ni H, Zuo JM, Chi M. Imaging Modulated Structure in EuAl4 using Cryogenic 4D-STEM. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2023; 29:1713. [PMID: 37613907 DOI: 10.1093/micmic/ozad067.885] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Affiliation(s)
- Haoyang Ni
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America
| | - Jian-Min Zuo
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
| | - Miaofang Chi
- Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America
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Simeth W, Bauer A, Franz C, Aqeel A, Bereciartua PJ, Sears JA, Francoual S, Back CH, Pfleiderer C. Resonant Elastic X-Ray Scattering of Antiferromagnetic Superstructures in EuPtSi_{3}. PHYSICAL REVIEW LETTERS 2023; 130:266701. [PMID: 37450805 DOI: 10.1103/physrevlett.130.266701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 04/06/2023] [Accepted: 05/11/2023] [Indexed: 07/18/2023]
Abstract
We report resonant elastic x-ray scattering of long-range magnetic order in EuPtSi_{3}, combining different scattering geometries with full linear polarization analysis to unambiguously identify magnetic scattering contributions. At low temperatures, EuPtSi_{3} stabilizes type A antiferromagnetism featuring various long-wavelength modulations. For magnetic fields applied in the hard magnetic basal plane, well-defined regimes of cycloidal, conical, and fanlike superstructures may be distinguished that encompass a pocket of commensurate type A order without superstructure. For magnetic field applied along the easy axis, the phase diagram comprises the cycloidal and conical superstructures only. Highlighting the power of polarized resonant elastic x-ray scattering, our results reveal a combination of magnetic phases that suggest a highly unusual competition between antiferromagnetic exchange interactions with Dzyaloshinsky-Moriya spin-orbit coupling of similar strength.
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Affiliation(s)
- Wolfgang Simeth
- Physik-Department, Technische Universität München, D-85748 Garching, Germany
- Laboratory for Neutron and Muon Instrumentation, Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - Andreas Bauer
- Physik-Department, Technische Universität München, D-85748 Garching, Germany
- Zentrum für QuantumEngineering (ZQE), Technische Universität München, D-85748 Garching, Germany
| | - Christian Franz
- Physik-Department, Technische Universität München, D-85748 Garching, Germany
- Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), D-85748 Garching, Germany
| | - Aisha Aqeel
- Physik-Department, Technische Universität München, D-85748 Garching, Germany
- Munich Center for Quantum Science and Technology (MCQST), Technische Universität München, D-85748 Garching, Germany
| | | | - Jennifer A Sears
- Deutsches Elektronen-Synchrotron (DESY), D-22607 Hamburg, Germany
| | - Sonia Francoual
- Deutsches Elektronen-Synchrotron (DESY), D-22607 Hamburg, Germany
| | - Christian H Back
- Physik-Department, Technische Universität München, D-85748 Garching, Germany
- Zentrum für QuantumEngineering (ZQE), Technische Universität München, D-85748 Garching, Germany
- Munich Center for Quantum Science and Technology (MCQST), Technische Universität München, D-85748 Garching, Germany
| | - Christian Pfleiderer
- Physik-Department, Technische Universität München, D-85748 Garching, Germany
- Zentrum für QuantumEngineering (ZQE), Technische Universität München, D-85748 Garching, Germany
- Munich Center for Quantum Science and Technology (MCQST), Technische Universität München, D-85748 Garching, Germany
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6
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One RA, Mican S, CimpoesȖu AG, Joldos M, Tetean R, Tiușan CV. Micromagnetic Design of Skyrmionic Materials and Chiral Magnetic Configurations in Patterned Nanostructures for Neuromorphic and Qubit Applications. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:4411. [PMID: 36558263 PMCID: PMC9782460 DOI: 10.3390/nano12244411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 12/02/2022] [Accepted: 12/06/2022] [Indexed: 06/17/2023]
Abstract
Our study addresses the problematics of magnetic skyrmions, nanometer-size vortex-like swirling topological defects, broadly studied today for applications in classic, neuromorphic and quantum information technologies. We tackle some challenging issues of material properties versus skyrmion stability and manipulation within a multiple-scale modeling framework, involving complementary ab-initio and micromagnetic frameworks. Ab-initio calculations provide insight into the anatomy of the magnetic anisotropy, the Dzyaloshinskii-Moriya asymmetric exchange interaction (DMI) and their response to a gating electric field. Various multi-layered heterostructures were specially designed to provide electric field tunable perpendicular magnetization and sizeable DMI, which are required for skyrmion occurrence. Landau-Lifshitz-Gilbert micromagnetic calculations in nanometric disks allowed the extraction of material parameter phase diagrams in which magnetic textures were classified according to their topological charge. We identified suitable ranges of magnetic anisotropy, DMI and saturation magnetization for stabilizing skyrmionic ground states or writing/manipulating them using either a spin-transfer torque of a perpendicular current or the electric field. From analyzing the different contributions to the total magnetic free energy, we point out some critical properties influencing the skyrmions' stability. Finally, we discuss some experimental issues related to the choice of materials or the design of novel magnetic materials compatible with skyrmionic applications.
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Affiliation(s)
- Roxana-Alina One
- Department of Condensed Matter Physics and Advanced Technologies, Faculty of Physics, Babeș-Bolyai University of Cluj-Napoca, 400084 Cluj-Napoca, Romania
| | - Sever Mican
- Department of Condensed Matter Physics and Advanced Technologies, Faculty of Physics, Babeș-Bolyai University of Cluj-Napoca, 400084 Cluj-Napoca, Romania
| | - Angela-Georgiana CimpoesȖu
- Department of Condensed Matter Physics and Advanced Technologies, Faculty of Physics, Babeș-Bolyai University of Cluj-Napoca, 400084 Cluj-Napoca, Romania
| | - Marius Joldos
- Computer Science Department, Faculty of Automation and Computer Science, Technical University of Cluj-Napoca, 400027 Cluj-Napoca, Romania
| | - Romulus Tetean
- Department of Condensed Matter Physics and Advanced Technologies, Faculty of Physics, Babeș-Bolyai University of Cluj-Napoca, 400084 Cluj-Napoca, Romania
| | - Coriolan Viorel Tiușan
- Department of Condensed Matter Physics and Advanced Technologies, Faculty of Physics, Babeș-Bolyai University of Cluj-Napoca, 400084 Cluj-Napoca, Romania
- National Center of Scientific Research, 54500 Vandoeuvre-lès-Nancy, France
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7
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Spitz L, Nomoto T, Kitou S, Nakao H, Kikkawa A, Francoual S, Taguchi Y, Arita R, Tokura Y, Arima TH, Hirschberger M. Entropy-Assisted, Long-Period Stacking of Honeycomb Layers in an AlB 2-Type Silicide. J Am Chem Soc 2022; 144:16866-16871. [PMID: 36066406 DOI: 10.1021/jacs.2c04995] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Configurational entropy can impact crystallization processes, tipping the scales between structures of nearly equal internal energy. Using alloyed single crystals of Gd2PdSi3 in the AlB2-type structure, we explore the formation of complex layer sequences made from alternating, two-dimensional triangular and honeycomb slabs. A four-period and an eight-period stacking sequence are found to be very close in internal energy, the latter being favored by entropy associated with covering the full configuration space of interlayer bonds. Possible consequences of polytype formation on magnetism in Gd2PdSi3 are discussed.
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Affiliation(s)
- Leonie Spitz
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
| | - Takuya Nomoto
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Shunsuke Kitou
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
| | - Hironori Nakao
- Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan
| | - Akiko Kikkawa
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
| | - Sonia Francoual
- Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany
| | - Yasujiro Taguchi
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
| | - Ryotaro Arita
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan.,Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Yoshinori Tokura
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan.,Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan.,Tokyo College, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Taka-Hisa Arima
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan.,Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
| | - Max Hirschberger
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan.,Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
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8
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Hayami S. Square skyrmion crystal in centrosymmetric systems with locally inversion-asymmetric layers. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:365802. [PMID: 35738246 DOI: 10.1088/1361-648x/ac7bcb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2022] [Accepted: 06/23/2022] [Indexed: 06/15/2023]
Abstract
We investigate an instability toward a square-lattice formation of magnetic skyrmions in centrosymmetric layered systems. By focusing on a bilayer square-lattice structure with the inversion center at the interlayer bond instead of the atomic site, we numerically examine the stability of the square skyrmion crystal (SkX) based on an effective spin model with the momentum-resolved interaction in the ground state through the simulated annealing. As a result, we find that a layer-dependent staggered Dzyaloshinskii-Moriya (DM) interaction built in the lattice structure becomes the origin of the square SkX in an external magnetic field irrespective of the sign of the interlayer exchange interaction. The obtained square SkX is constituted of the SkXs with different helicities in each layer due to the staggered DM interaction. Furthermore, we show that the interplay between the staggered DM interaction and the interlayer exchange interaction gives rise to a double-Qstate with a uniform component of the scalar chirality in the low-field region. The present results provide another way of stabilizing the square SkX in centrosymmetric magnets, which will be useful to explore further exotic topological spin textures.
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Affiliation(s)
- Satoru Hayami
- Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
- Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
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9
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Optimization of physical quantities in the autoencoder latent space. Sci Rep 2022; 12:9003. [PMID: 35637207 PMCID: PMC9151681 DOI: 10.1038/s41598-022-13007-5] [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: 02/09/2022] [Accepted: 05/18/2022] [Indexed: 11/24/2022] Open
Abstract
We propose a strategy for optimizing physical quantities based on exploring in the latent space of a variational autoencoder (VAE). We train a VAE model using various spin configurations formed on a two-dimensional chiral magnetic system. Three optimization algorithms are used to explore the latent space of the trained VAE. The first algorithm, the single-code modification algorithm, is designed for improving the local energetic stability of spin configurations to generate physically plausible spin states. The other two algorithms, the genetic algorithm and the stochastic algorithm, aim to optimize the global physical quantities, such as topological index, magnetization, energy, and directional correlation. The advantage of our method is that various optimization algorithms can be applied in the latent space containing the abstracted representation constructed by the trained VAE model. Our method based on latent space exploration is utilized for efficient physical quantity optimization.
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