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Garanin DA, Chudnovsky EM. Random anisotropy magnet at finite temperature. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:285801. [PMID: 35439745 DOI: 10.1088/1361-648x/ac684a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Accepted: 04/19/2022] [Indexed: 06/14/2023]
Abstract
We present finite-temperature Monte Carlo studies of a 2D random-anisotropy (RA) magnet on lattices containing one million spins. The correlated spin-glass state predicted by analytical theories is reproduced in simulations, as are the field-cooled and zero-field-cooled magnetization curves observed in experiments. The orientations of lattice spins begin to freeze when the temperature is lowered. The freezing transition is due to the energy barriers generated by the RA rather than due to random interactions in conventional spin-glasses. We describe freezing by introducing the time-dependent spin-glass order parameterqand the spin-melting timeτMdefined viaq=τM/tabove freezing, wheretis the time of the experiment represented by the number of Monte Carlo steps.
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Affiliation(s)
- Dmitry A Garanin
- Physics Department, Herbert H Lehman College and Graduate School, The City University of New York, 250 Bedford Park Boulevard West, Bronx, NY 10468-1589, United States of America
| | - Eugene M Chudnovsky
- Physics Department, Herbert H Lehman College and Graduate School, The City University of New York, 250 Bedford Park Boulevard West, Bronx, NY 10468-1589, United States of America
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Martin N, Bannenberg LJ, Deutsch M, Pappas C, Chaboussant G, Cubitt R, Mirebeau I. Field-induced vortex-like textures as a probe of the critical line in reentrant spin glasses. Sci Rep 2021; 11:20753. [PMID: 34675354 PMCID: PMC8531314 DOI: 10.1038/s41598-021-99860-2] [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: 05/18/2021] [Accepted: 09/29/2021] [Indexed: 11/09/2022] Open
Abstract
We study the evolution of the low-temperature field-induced magnetic defects observed under an applied magnetic field in a series of frustrated amorphous ferromagnets (Fe\documentclass[12pt]{minimal}
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\begin{document}$$_{x}$$\end{document}x”). Combining small-angle neutron scattering and Monte Carlo simulations, we show that the morphology of these defects resemble that of quasi-bidimensional spin vortices. They are observed in the so-called “reentrant” spin-glass (RSG) phase, up to the critical concentration \documentclass[12pt]{minimal}
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\begin{document}$$x_{\mathrm{C}} \approx 0.36$$\end{document}xC≈0.36 which separates the RSG and “true” spin glass (SG) within the low temperature part of the magnetic phase diagram of a-Fe1−xMnx. These textures systematically decrease in size with increasing magnetic field or decreasing the average exchange interaction, and they finally disappear in the SG sample (\documentclass[12pt]{minimal}
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\begin{document}$$x = 0.41$$\end{document}x=0.41), being replaced by field-induced correlations over finite length scales. We argue that the study of these nanoscopic defects could be used to probe the critical line between the RSG and SG phases.
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Affiliation(s)
- N Martin
- Université Paris-Saclay, CNRS, CEA, Laboratoire Léon Brillouin, 91191, Gif-sur-Yvette, France.
| | - L J Bannenberg
- Faculty of Applied Science, Delft University of Technology, 2629 JB, Delft, The Netherlands
| | - M Deutsch
- CNRS, CRM2, Université de Lorraine, Nancy, France
| | - C Pappas
- Faculty of Applied Science, Delft University of Technology, 2629 JB, Delft, The Netherlands
| | - G Chaboussant
- Université Paris-Saclay, CNRS, CEA, Laboratoire Léon Brillouin, 91191, Gif-sur-Yvette, France
| | - R Cubitt
- Institut Laue Langevin, BP156, 38042, Grenoble, France
| | - I Mirebeau
- Université Paris-Saclay, CNRS, CEA, Laboratoire Léon Brillouin, 91191, Gif-sur-Yvette, France
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Capic D, Garanin DA, Chudnovsky EM. Skyrmion-skyrmion interaction in a magnetic film. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:415803. [PMID: 32526724 DOI: 10.1088/1361-648x/ab9bc8] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 06/11/2020] [Indexed: 06/11/2023]
Abstract
Interaction of two skyrmions stabilized by the ferromagnetic exchange, Dzyaloshinskii-Moriya interaction (DMI), and external magnetic field has been studied numerically on a 2D lattice of size large compared to the separation,d, between the skyrmions. We show that two skyrmions of the same chirality (determined by the symmetry of the crystal) repel. In accordance with earlier analytical results, their long-range pair interaction falls out with the separation as exp(-d/δH), whereδHis the magnetic screening length, independent of the DMI. The prefactor in this expression depends on the DMI that drives the repulsion. The latter results in the spiral motion of the two skyrmions around each other, with the separation between them growing logarithmically with time. When two skyrmions of the total topological chargeQ= 2 are pushed close to each other, the discreteness of the atomic lattice makes them collapse into one skyrmion of chargeQ= 1 below a critical separation. Experiment is proposed that would allow one to measure the interaction between two skyrmions by holding them in positions with two magnetic tips. Our findings should be of value for designing topologically protected magnetic memory based upon skyrmions.
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Affiliation(s)
- D Capic
- Physics Department, Herbert H. Lehman College and Graduate School, The City University of New York, 250 Bedford Park Boulevard West, Bronx, New York 10468-1589, United States of America
| | - D A Garanin
- Physics Department, Herbert H. Lehman College and Graduate School, The City University of New York, 250 Bedford Park Boulevard West, Bronx, New York 10468-1589, United States of America
| | - E M Chudnovsky
- Physics Department, Herbert H. Lehman College and Graduate School, The City University of New York, 250 Bedford Park Boulevard West, Bronx, New York 10468-1589, United States of America
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Volovik GE, Rysti J, Mäkinen JT, Eltsov VB. Spin, Orbital, Weyl and Other Glasses in Topological Superfluids. JOURNAL OF LOW TEMPERATURE PHYSICS 2018; 196:82-101. [PMID: 31274926 PMCID: PMC6570685 DOI: 10.1007/s10909-018-02132-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/23/2018] [Accepted: 12/15/2018] [Indexed: 06/09/2023]
Abstract
One of the most spectacular discoveries made in superfluid3 He confined in a nanostructured material like aerogel or nafen was the observation of the destruction of the long-range orientational order by a weak random anisotropy. The quenched random anisotropy provided by the confining material strands produces several different glass states resolved in NMR experiments in the chiral superfluid3 He-A and in the time-reversal-invariant polar phase. The smooth textures of spin and orbital order parameters in these glasses can be characterized in terms of the randomly distributed topological charges, which describe skyrmions, spin vortices and hopfions. In addition, in these skyrmion glasses the momentum-space topological invariants are randomly distributed in space. The Chern mosaic, Weyl glass, torsion glass and other exotic topological states are examples of close connections between the real-space and momentum-space topologies in superfluid3 He phases in aerogel.
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Affiliation(s)
- G. E. Volovik
- Department of Applied Physics, Aalto University, P.O. Box 15100, 00076 Aalto, Finland
- Landau Institute for Theoretical Physics, Acad. Semyonov Av., 1a, Chernogolovka, Russia 142432
| | - J. Rysti
- Department of Applied Physics, Aalto University, P.O. Box 15100, 00076 Aalto, Finland
| | - J. T. Mäkinen
- Department of Applied Physics, Aalto University, P.O. Box 15100, 00076 Aalto, Finland
| | - V. B. Eltsov
- Department of Applied Physics, Aalto University, P.O. Box 15100, 00076 Aalto, Finland
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