1
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Tang N, Liyanage WLNC, Montoya SA, Patel S, Quigley LJ, Grutter AJ, Fitzsimmons MR, Sinha S, Borchers JA, Fullerton EE, DeBeer-Schmitt L, Gilbert DA. Skyrmion-Excited Spin-Wave Fractal Networks. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2300416. [PMID: 37139924 DOI: 10.1002/adma.202300416] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Revised: 04/24/2023] [Indexed: 05/05/2023]
Abstract
Magnetic skyrmions exhibit unique, technologically relevant pseudo-particle behaviors which arise from their topological protection, including well-defined, 3D dynamic modes that occur at microwave frequencies. During dynamic excitation, spin waves are ejected into the interstitial regions between skyrmions, creating the magnetic equivalent of a turbulent sea. However, since the spin waves in these systems have a well-defined length scale, and the skyrmions are on an ordered lattice, ordered structures from spin-wave interference can precipitate from the chaos. This work uses small-angle neutron scattering (SANS) to capture the dynamics in hybrid skyrmions and investigate the spin-wave structure. Performing simultaneous ferromagnetic resonance and SANS, the diffraction pattern shows a large increase in low-angle scattering intensity, which is present only in the resonance condition. This scattering pattern is best fit using a mass fractal model, which suggests the spin waves form a long-range fractal network. The fractal structure is constructed of fundamental units with a size that encodes the spin-wave emissions and are constrained by the skyrmion lattice. These results offer critical insights into the nanoscale dynamics of skyrmions, identify a new dynamic spin-wave fractal structure, and demonstrate SANS as a unique tool to probe high-speed dynamics.
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Affiliation(s)
- Nan Tang
- Materials Science and Engineering Department, University of Tennessee, Knoxville, TN, 37996, USA
| | - W L N C Liyanage
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, 37996, USA
| | - Sergio A Montoya
- Center for Memory and Recording Research, University of California, San Diego, La Jolla, CA, 92093, USA
- Naval Information Warfare Center Pacific, San Diego, CA, 92152, USA
| | - Sheena Patel
- Center for Memory and Recording Research, University of California, San Diego, La Jolla, CA, 92093, USA
- Physics Department, University of California, San Diego, San Diego, CA, 92093, USA
| | - Lizabeth J Quigley
- Materials Science and Engineering Department, University of Tennessee, Knoxville, TN, 37996, USA
| | - Alexander J Grutter
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - Michael R Fitzsimmons
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, 37996, USA
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Sunil Sinha
- Physics Department, University of California, San Diego, San Diego, CA, 92093, USA
| | - Julie A Borchers
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - Eric E Fullerton
- Center for Memory and Recording Research, University of California, San Diego, La Jolla, CA, 92093, USA
- Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, CA, 92093, USA
| | - Lisa DeBeer-Schmitt
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Dustin A Gilbert
- Materials Science and Engineering Department, University of Tennessee, Knoxville, TN, 37996, USA
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, 37996, USA
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2
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Omnidirectional flat bands in chiral magnonic crystals. Sci Rep 2022; 12:17831. [PMID: 36284121 PMCID: PMC9596476 DOI: 10.1038/s41598-022-20539-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Accepted: 09/14/2022] [Indexed: 11/08/2022] Open
Abstract
The magnonic band structure of two-dimensional chiral magnonic crystals is theoretically investigated. The proposed metamaterial involves a three-dimensional architecture, where a thin ferromagnetic layer is in contact with a two-dimensional periodic array of heavy-metal square islands. When these two materials are in contact, an anti-symmetric exchange coupling known as the Dzyaloshinskii–Moriya interaction (DMI) arises, which generates nonreciprocal spin waves and chiral magnetic order. The Landau–Lifshitz equation and the plane-wave method are employed to study the dynamic magnetic behavior. A systematic variation of geometric parameters, the DMI constant, and the filling fraction allows the examination of spin-wave propagation features, such as the spatial profiles of the dynamic magnetization, the isofrequency contours, and group velocities. In this study, it is found that omnidirectional flat magnonic bands are induced by a sufficiently strong Dzyaloshinskii–Moriya interaction underneath the heavy-metal islands, where the spin excitations are active. The theoretical results were substantiated by micromagnetic simulations. These findings are relevant for envisioning applications associated with spin-wave-based logic devices, where the nonreciprocity and channeling of the spin waves are of fundamental and practical scientific interest.
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3
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Sekiguchi F, Budzinauskas K, Padmanabhan P, Versteeg RB, Tsurkan V, Kézsmárki I, Foggetti F, Artyukhin S, van Loosdrecht PHM. Slowdown of photoexcited spin dynamics in the non-collinear spin-ordered phases in skyrmion host GaV 4S 8. Nat Commun 2022; 13:3212. [PMID: 35680864 PMCID: PMC9184521 DOI: 10.1038/s41467-022-30829-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Accepted: 05/20/2022] [Indexed: 11/10/2022] Open
Abstract
Formation of magnetic order alters the character of spin excitations, which then affects transport properties. We investigate the photoexcited ultrafast spin dynamics in different magnetic phases in Néel-type skyrmion host GaV4S8 with time-resolved magneto-optical Kerr effect experiments. The coherent spin precession, whose amplitude is enhanced in the skyrmion-lattice phase, shows a signature of phase coexistence across the magnetic phase transitions. The incoherent spin relaxation dynamics slows down by a factor of two in the skyrmion-lattice/cycloid phases, indicating significant decrease in thermal conductivity triggered by a small change of magnetic field. The slow heat diffusion in the skyrmion-lattice/cycloid phases is attributed to the stronger magnon scattering off the domain walls formed in abundance in the skyrmion-lattice/cycloid phase. These results highlight the impact of spatial spin structure on the ultrafast heat transport in spin systems, providing a useful insight for the step toward ultrafast photocontrol of the magnets with novel spin orders. Skyrmions are a topological magnetic texture that have garnered considerable interest for various technological applications. Here, Sekiguchi et al. investigate the ultrafast optical response of GaV4S6, and find a significant reduction in the thermal conductivity in the skyrmion phase.
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Affiliation(s)
- Fumiya Sekiguchi
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937, Köln, Germany.
| | - Kestutis Budzinauskas
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937, Köln, Germany
| | - Prashant Padmanabhan
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937, Köln, Germany
| | - Rolf B Versteeg
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937, Köln, Germany
| | - Vladimir Tsurkan
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159, Augsburg, Germany.,Institute of Applied Physics, MD 2028, Chișinău, Republic of Moldova
| | - István Kézsmárki
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159, Augsburg, Germany
| | - Francesco Foggetti
- Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genova, Italy.,Dipartimento di Fisica, Università di Genova, Via Dodecaneso, 33, 16146, Genova, Italy
| | - Sergey Artyukhin
- Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genova, Italy
| | - Paul H M van Loosdrecht
- II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937, Köln, Germany.
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4
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Weber T, Fobes DM, Waizner J, Steffens P, Tucker GS, Böhm M, Beddrich L, Franz C, Gabold H, Bewley R, Voneshen D, Skoulatos M, Georgii R, Ehlers G, Bauer A, Pfleiderer C, Böni P, Janoschek M, Garst M. Topological magnon band structure of emergent Landau levels in a skyrmion lattice. Science 2022; 375:1025-1030. [PMID: 35239388 DOI: 10.1126/science.abe4441] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The motion of a spin excitation across topologically nontrivial magnetic order exhibits a deflection that is analogous to the effect of the Lorentz force on an electrically charged particle in an orbital magnetic field. We used polarized inelastic neutron scattering to investigate the propagation of magnons (i.e., bosonic collective spin excitations) in a lattice of skyrmion tubes in manganese silicide. For wave vectors perpendicular to the skyrmion tubes, the magnon spectra are consistent with the formation of finely spaced emergent Landau levels that are characteristic of the fictitious magnetic field used to account for the nontrivial topological winding of the skyrmion lattice. This provides evidence of a topological magnon band structure in reciprocal space, which is borne out of the nontrivial real-space topology of a magnetic order.
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Affiliation(s)
- T Weber
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - D M Fobes
- Los Alamos National Laboratory, Los Alamos, NM, USA
| | - J Waizner
- Institut für Theoretische Physik, Universität zu Köln, 50937 Köln, Germany
| | - P Steffens
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - G S Tucker
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen, Switzerland.,Laboratory for Quantum Magnetism, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - M Böhm
- Institut Laue-Langevin, CS 20156, 38042 Grenoble Cedex 9, France
| | - L Beddrich
- Physik-Department, Technische Universität München, 85748 Garching, Germany.,MLZ, Technische Universität München, 85748 Garching, Germany
| | - C Franz
- Physik-Department, Technische Universität München, 85748 Garching, Germany.,MLZ, Technische Universität München, 85748 Garching, Germany
| | - H Gabold
- Physik-Department, Technische Universität München, 85748 Garching, Germany.,MLZ, Technische Universität München, 85748 Garching, Germany
| | - R Bewley
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK
| | - D Voneshen
- ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK.,Department of Physics, Royal Holloway University of London, Egham TW20 0EX, UK
| | - M Skoulatos
- Physik-Department, Technische Universität München, 85748 Garching, Germany.,MLZ, Technische Universität München, 85748 Garching, Germany
| | - R Georgii
- Physik-Department, Technische Universität München, 85748 Garching, Germany.,MLZ, Technische Universität München, 85748 Garching, Germany
| | - G Ehlers
- Neutron Technologies Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - A Bauer
- Physik-Department, Technische Universität München, 85748 Garching, Germany.,Centre for Quantum Engineering (ZQE), Technische Universität München, 85748 Garching, Germany
| | - C Pfleiderer
- Physik-Department, Technische Universität München, 85748 Garching, Germany.,Centre for Quantum Engineering (ZQE), Technische Universität München, 85748 Garching, Germany.,MCQST, Technische Universität München, 85748 Garching, Germany
| | - P Böni
- Physik-Department, Technische Universität München, 85748 Garching, Germany
| | - M Janoschek
- Los Alamos National Laboratory, Los Alamos, NM, USA.,Laboratory for Neutron and Muon Instrumentation (LIN), Paul Scherrer Institute, CH-5232 Villigen, Switzerland.,Physik-Institut, Universität Zürich, CH-8057 Zürich, Switzerland
| | - M Garst
- Institut für Theoretische Physik, Universität zu Köln, 50937 Köln, Germany.,Institut für Theoretische Physik, Technische Universität Dresden, 01062 Dresden, Germany.,Institut für Theoretische Festkörperphysik, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany.,Institute for Quantum Materials and Technology, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
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5
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Abstract
Nonreciprocity emerges in nature and in artificial objects from various physical origins, being widely utilized in contemporary technologies as exemplified by diode elements in electronics. While most of the nonreciprocal phenomena are realized by employing interfaces where the inversion symmetry is trivially lifted, nonreciprocal transport of photons, electrons, magnons, and possibly phonons also emerge in bulk crystals with broken space inversion and time reversal symmetries. Among them, directional propagation of bulk magnons (i.e., quanta of spin wave excitation) is attracting much attention nowadays for its potentially large nonreciprocity suitable for spintronic and spin-caloritronic applications. Here, we demonstrate nonreciprocal propagation of spin waves for the conical spin helix state in Cu2OSeO3 due to a combination of dipole and Dzyaloshinskii-Moriya interactions. The observed nonreciprocal spin dispersion smoothly connects to the hitherto known magnetochiral nonreciprocity in the field-induced collinear spin state; thus, all the spin phases show diode characteristics in this chiral insulator.
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6
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Luo Y, Marcus GG, Trump BA, Kindervater J, Stone MB, Rodriguez-Rivera JA, Qiu Y, McQueen TM, Tchernyshyov O, Broholm C. Low-energy magnons in the chiral ferrimagnet Cu 2OSeO 3: A coarse-grained approach. PHYSICAL REVIEW. B 2020; 101:10.1103/PhysRevB.101.144411. [PMID: 33655091 PMCID: PMC7919739 DOI: 10.1103/physrevb.101.144411] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We report a comprehensive neutron scattering study of low energy magnetic excitations in the breathing pyrochlore helimagnetic Cu2OSeO3. Fully documenting the four lowest energy magnetic modes that leave the ferrimagnetic configuration of the "strong tetrahedra" intact ( | ℏ ω | < 13 meV), we find gapless quadratic dispersion at the point for energies above 0.2 meV, two doublets separated by 1.6(2) meV at the R point, and a bounded continuum at the X point. Our constrained rigid spin cluster model relates these features to Dzyaloshinskii-Moriya (DM) interactions and the incommensurate helical ground state. Combining conventional spin wave theory with a spin cluster form factor accurately reproduces the measured equal time structure factor through multiple Brillouin zones. An effective spin Hamiltonian describing complex anisotropic intercluster interactions is obtained.
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Affiliation(s)
- Yi Luo
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - G. G. Marcus
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - B. A. Trump
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA
| | - J. Kindervater
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - M. B. Stone
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - J. A. Rodriguez-Rivera
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA
- Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
| | - Yiming Qiu
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA
| | - T. M. McQueen
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - O. Tchernyshyov
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - C. Broholm
- Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
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7
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Abstract
Since the late 1970s, MnSi has played a major role in developing the theory of helical magnets in non-centrosymmetric materials showing the Dzyaloshinsky-Moriya interaction (DMI). With a long helimagnetic pitch of 175 Å as compared to the lattice d-spacing of 4.55 Å, it was ideal for performing neutron studies, especially as large single crystals could be grown. A (B-T)-phase diagram was measured, and in these studies, under the application of a field of about 180 mT perpendicular to the scattering vector Q, a so-called A-phase in the B-T phase diagram was found and first interpreted as a re-orientation of the magnetic helix. After the surprising discovery of the skyrmion lattice in the A-phase in 2009, much interest arose due to the rigidity of the skyrmionic lattice, which is only loosely bound to the crystal lattice, and therefore only relatively small current densities can already induce a motion of this lattice. A very interesting approach to even better understand the complex structures in the phase diagram is to measure and model the spin excitations in MnSi. As the helimagnetic state is characterized by a long pitch of about 175 Å, the associated characteristic excitations form a band structure due to Umklapp scattering and can only be observed at very small Q with energies below 1 meV. Similarly, the excitations of the skyrmion lattice are very soft and low-energetic. We investigated the magnons in MnSi in the whole (B,T)-phase diagram starting in the single-k helimagnetic state by applying a small magnetic field, B = 100 mT. This way, the complexity of the magnon spectrum is significantly reduced, allowing for a detailed comparison of the data with theory, resulting in a full theoretical understanding of the spin system of MnSi in all its different magnetic phases.
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8
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Gallardo RA, Cortés-Ortuño D, Schneider T, Roldán-Molina A, Ma F, Troncoso RE, Lenz K, Fangohr H, Lindner J, Landeros P. Flat Bands, Indirect Gaps, and Unconventional Spin-Wave Behavior Induced by a Periodic Dzyaloshinskii-Moriya Interaction. PHYSICAL REVIEW LETTERS 2019; 122:067204. [PMID: 30822086 DOI: 10.1103/physrevlett.122.067204] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 10/26/2018] [Indexed: 06/09/2023]
Abstract
Periodically patterned metamaterials are known for exhibiting wave properties similar to the ones observed in electronic band structures in crystal lattices. In particular, periodic ferromagnetic materials are characterized by the presence of bands and band gaps in their spin-wave spectrum at tunable GHz frequencies. Recently, the fabrication of magnets hosting Dzyaloshinskii-Moriya interactions has been pursued with high interest since properties, such as the stabilization of chiral spin textures and nonreciprocal spin-wave propagation, emerge from this antisymmetric exchange coupling. In this context, to further engineer the magnon band structure, we propose the implementation of magnonic crystals with periodic Dzyaloshinskii-Moriya interactions, which can be obtained, for instance, via patterning of periodic arrays of heavy metal wires on top of an ultrathin magnetic film. We demonstrate through theoretical calculations and micromagnetic simulations that such systems show an unusual evolution of the standing spin waves around the gaps. We also predict the emergence of indirect gaps and flat bands, effects that depend on the strength of the Dzyaloshinskii-Moriya interaction. Such phenomena, which have been previously observed in different systems, are observed here simultaneously, opening new routes towards engineered metamaterials for spin-wave-based devices.
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Affiliation(s)
- R A Gallardo
- Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile
- Center for the Development of Nanoscience and Nanotechnology (CEDENNA), 917-0124 Santiago, Chile
| | - D Cortés-Ortuño
- Faculty of Engineering and Physical Sciences, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | - T Schneider
- Helmholtz-Zentrum Dresden-Rossendorf, Institut of Ion Beam Physics and Materials Research, Bautzner Landstr. 400, 01328 Dresden, Germany
- Department of Physics, Technische Universität Chemnitz, Reichenhainer Str. 70, 09126 Chemnitz, Germany
| | - A Roldán-Molina
- Universidad de Aysén, Calle Obispo Vielmo 62, Coyhaique, Chile
| | - Fusheng Ma
- Jiangsu Key Lab on Opto-Electronic Technology, Center for Quantum Transport and Thermal Energy Science, School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China
| | - R E Troncoso
- Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile
- Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - K Lenz
- Helmholtz-Zentrum Dresden-Rossendorf, Institut of Ion Beam Physics and Materials Research, Bautzner Landstr. 400, 01328 Dresden, Germany
| | - H Fangohr
- Faculty of Engineering and Physical Sciences, University of Southampton, Southampton SO17 1BJ, United Kingdom
- European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Germany
| | - J Lindner
- Helmholtz-Zentrum Dresden-Rossendorf, Institut of Ion Beam Physics and Materials Research, Bautzner Landstr. 400, 01328 Dresden, Germany
| | - P Landeros
- Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile
- Center for the Development of Nanoscience and Nanotechnology (CEDENNA), 917-0124 Santiago, Chile
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9
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Weiler M, Aqeel A, Mostovoy M, Leonov A, Geprägs S, Gross R, Huebl H, Palstra TTM, Goennenwein STB. Helimagnon Resonances in an Intrinsic Chiral Magnonic Crystal. PHYSICAL REVIEW LETTERS 2017; 119:237204. [PMID: 29286698 DOI: 10.1103/physrevlett.119.237204] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Indexed: 06/07/2023]
Abstract
We experimentally study magnetic resonances in the helical and conical magnetic phases of the chiral magnetic insulator Cu_{2}OSeO_{3} at the temperature T=5 K. Using a broadband microwave spectroscopy technique based on vector network analysis, we identify three distinct sets of helimagnon resonances in the frequency range 2 GHz≤f≤20 GHz with low magnetic damping α≤0.003. The extracted resonance frequencies are in accordance with calculations of the helimagnon band structure found in an intrinsic chiral magnonic crystal. The periodic modulation of the equilibrium spin direction that leads to the formation of the magnonic crystal is a direct consequence of the chiral magnetic ordering caused by the Dzyaloshinskii-Moriya interaction. The mode coupling in the magnonic crystal allows excitation of helimagnons with wave vectors that are multiples of the spiral wave vector.
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Affiliation(s)
- Mathias Weiler
- Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
- Physik-Department, Technische Universität München, 85748 Garching, Germany
| | - Aisha Aqeel
- Zernike Institute for Advanced Materials, University of Groningen, 9700 AB Groningen, The Netherlands
| | - Maxim Mostovoy
- Zernike Institute for Advanced Materials, University of Groningen, 9700 AB Groningen, The Netherlands
| | - Andrey Leonov
- Zernike Institute for Advanced Materials, University of Groningen, 9700 AB Groningen, The Netherlands
- Center for Chiral Science, Hiroshima University, Hiroshima 739-8526, Japan
| | - Stephan Geprägs
- Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
| | - Rudolf Gross
- Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
- Physik-Department, Technische Universität München, 85748 Garching, Germany
- Nanosystems Initiative Munich, 80799 Munich, Germany
| | - Hans Huebl
- Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
- Physik-Department, Technische Universität München, 85748 Garching, Germany
- Nanosystems Initiative Munich, 80799 Munich, Germany
| | - Thomas T M Palstra
- Zernike Institute for Advanced Materials, University of Groningen, 9700 AB Groningen, The Netherlands
| | - Sebastian T B Goennenwein
- Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
- Physik-Department, Technische Universität München, 85748 Garching, Germany
- Nanosystems Initiative Munich, 80799 Munich, Germany
- Institut für Festkörper- und Materialphysik, Technische Universität Dresden, 01062 Dresden, Germany
- Center for Transport and Devices of Emergent Materials, Technische Universität Dresden, 01062 Dresden, Germany
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10
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Van Lich L, Shimada T, Wang J, Kitamura T. Self-ordering of nontrivial topological polarization structures in nanoporous ferroelectrics. NANOSCALE 2017; 9:15525-15533. [PMID: 28980678 DOI: 10.1039/c7nr04661h] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Topological field structures, such as skyrmions, merons, and vortices, are important features found in ordered systems with spontaneously broken symmetry. A plethora of topological field structures have been discovered in magnetic and ordered soft matter systems due to the presence of inherent chiral interactions, and this has provided a fruitful platform for unearthing additional groundbreaking functionalities. However, despite being one of the most important classes of ordered systems, ferroelectrics scarcely form topological polarization structures due to their lack of intrinsic chiral interactions. In the present study, we demonstrate using multiphysics phase-field modelling based on the Ginzburg-Landau theory that a rich assortment of nontrivial topological polarization structures, including hedgehogs, antivortices, multidirectional vortices, and vortex arrays, can be spontaneously formed in three-dimensional nanoporous ferroelectric structures. We realize that confining ferroelectrics to trivial geometries that are incompatible with the orientation symmetry may impose extrinsic frustration to the polarization field through the enhancement of depolarization fields at free porous surfaces. This frustration gives rise to symmetry breaking, resulting in the formation of nontrivial topological polarization structures as the ground state. We further topologically characterize the local accommodation of polarization structures by viewing them in a new perspective, in which polarization ordering can be mapped on the order parameter space, according to the topological theory of defects and homotopy theory. The results indicate that the nanoporous structures contain composite topological objects composed of two or more elementary topological polarization structures. The present study therefore offers a playground for exploring novel physical phenomena in ferroelectric systems as well as a novel nanoelectronics characterization platform for future topology-based nanotechnologies.
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Affiliation(s)
- Le Van Lich
- Department of Mechanical Engineering and Science, Kyoto University, Nishikyo-ku, Kyoto 615-8540, Japan.
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11
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Dussaux A, Schoenherr P, Koumpouras K, Chico J, Chang K, Lorenzelli L, Kanazawa N, Tokura Y, Garst M, Bergman A, Degen CL, Meier D. Local dynamics of topological magnetic defects in the itinerant helimagnet FeGe. Nat Commun 2016; 7:12430. [PMID: 27535899 PMCID: PMC4992142 DOI: 10.1038/ncomms12430] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 07/01/2016] [Indexed: 11/24/2022] Open
Abstract
Chiral magnetic interactions induce complex spin textures including helical and conical spin spirals, as well as particle-like objects such as magnetic skyrmions and merons. These spin textures are the basis for innovative device paradigms and give rise to exotic topological phenomena, thus being of interest for both applied and fundamental sciences. Present key questions address the dynamics of the spin system and emergent topological defects. Here we analyse the micromagnetic dynamics in the helimagnetic phase of FeGe. By combining magnetic force microscopy, single-spin magnetometry and Landau–Lifschitz–Gilbert simulations we show that the nanoscale dynamics are governed by the depinning and subsequent motion of magnetic edge dislocations. The motion of these topologically stable objects triggers perturbations that can propagate over mesoscopic length scales. The observation of stochastic instabilities in the micromagnetic structure provides insight to the spatio-temporal dynamics of itinerant helimagnets and topological defects, and discloses open challenges regarding their technological usage. Topological defects may strongly influence the evolution of a materials' micromagnetic structure whilst their manipulation forms the basis for emerging technological concepts. Here, the authors study the depinning and motion of magnetic edge dislocations in the domain structure of helimagnetic FeGe.
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Affiliation(s)
- A Dussaux
- Department of Physics, ETH Zürich, Otto Stern Weg 1, Zurich 8093, Switzerland
| | - P Schoenherr
- Department of Materials, ETH Zürich, Vladimir-Prelog-Weg 4, Zurich 8093, Switzerland
| | - K Koumpouras
- Department of Physics and Astronomy, Uppsala University, PO Box 516, Uppsala 75120, Sweden
| | - J Chico
- Department of Physics and Astronomy, Uppsala University, PO Box 516, Uppsala 75120, Sweden
| | - K Chang
- Department of Physics, ETH Zürich, Otto Stern Weg 1, Zurich 8093, Switzerland
| | - L Lorenzelli
- Department of Physics, ETH Zürich, Otto Stern Weg 1, Zurich 8093, Switzerland
| | - N Kanazawa
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
| | - Y Tokura
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan.,RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - M Garst
- Institute for Theoretical Physics, Universität zu Köln, Köln D-50937, Germany
| | - A Bergman
- Department of Physics and Astronomy, Uppsala University, PO Box 516, Uppsala 75120, Sweden
| | - C L Degen
- Department of Physics, ETH Zürich, Otto Stern Weg 1, Zurich 8093, Switzerland
| | - D Meier
- Department of Materials, ETH Zürich, Vladimir-Prelog-Weg 4, Zurich 8093, Switzerland.,Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim 7491, Norway
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Magnon spectrum of the helimagnetic insulator Cu2OSeO3. Nat Commun 2016; 7:10725. [PMID: 26911567 PMCID: PMC4773425 DOI: 10.1038/ncomms10725] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Accepted: 01/14/2016] [Indexed: 11/08/2022] Open
Abstract
Complex low-temperature-ordered states in chiral magnets are typically governed by a competition between multiple magnetic interactions. The chiral-lattice multiferroic Cu2OSeO3 became the first insulating helimagnetic material in which a long-range order of topologically stable spin vortices known as skyrmions was established. Here we employ state-of-the-art inelastic neutron scattering to comprehend the full three-dimensional spin-excitation spectrum of Cu2OSeO3 over a broad range of energies. Distinct types of high- and low-energy dispersive magnon modes separated by an extensive energy gap are observed in excellent agreement with the previously suggested microscopic theory based on a model of entangled Cu4 tetrahedra. The comparison of our neutron spectroscopy data with model spin-dynamical calculations based on these theoretical proposals enables an accurate quantitative verification of the fundamental magnetic interactions in Cu2OSeO3 that are essential for understanding its abundant low-temperature magnetically ordered phases.
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