51
|
Deger C. Strain-enhanced Dzyaloshinskii-Moriya interaction at Co/Pt interfaces. Sci Rep 2020; 10:12314. [PMID: 32704010 PMCID: PMC7378838 DOI: 10.1038/s41598-020-69360-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 07/10/2020] [Indexed: 11/08/2022] Open
Abstract
The interfacial Dzyaloshinskii-Moriya interaction (DMI) is an essential ingredient for stabilizing chiral spin configurations in spintronic applications. Here, via first-principles calculations, we reveal the influence of lattice strain on DMI in Co/Pt interface. We observed a considerable enhancement for a certain lattice strain. Furthermore, a direct correlation is established between the DMI and interlayer distances dominated by the strain, which is attributed to a hybridization of electronic orbitals. This hybridization has also been presented as the microscopic origin of the interfacial DMI. We anticipate that our predictions provide new insights into the control of interfacial DMI for skyrmion-based spintronic devices.
Collapse
Affiliation(s)
- Caner Deger
- Department of Physics, Marmara University, 34722, Ziverbey, Istanbul, Turkey.
| |
Collapse
|
52
|
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.
Collapse
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
| |
Collapse
|
53
|
Rendell-Bhatti F, Lamb RJ, van der Jagt JW, Paterson GW, Swagten HJM, McGrouther D. Spontaneous creation and annihilation dynamics and strain-limited stability of magnetic skyrmions. Nat Commun 2020; 11:3536. [PMID: 32669654 PMCID: PMC7363836 DOI: 10.1038/s41467-020-17338-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Accepted: 06/24/2020] [Indexed: 11/08/2022] Open
Abstract
Magnetic skyrmions are topological magnetic spin structures exhibiting particle-like behaviour. They are of strong interest from a fundamental viewpoint and for application, where they have potential to act as information carriers in future low-power computing technologies. Importantly, skyrmions have high physical stability because of topological protection. However, they have potential to deform according to their local energy environment. Here we demonstrate that, in regions of high exchange energy density, skyrmions may exhibit such extreme deformation that spontaneous merging with nearest neighbours or spawning new skyrmions is favoured to attain a lower energy state. Using transmission electron microscopy and a high-speed imaging detector, we observe dynamics involving distinct configurational states, in which transitions are accompanied by spontaneous creation or annihilation of skyrmions. These observations raise important questions regarding the limits of skyrmion stability and topological charge conservation, while also suggesting a means of control of skyrmion creation and annihilation.
Collapse
Affiliation(s)
| | - Raymond J Lamb
- SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Johannes W van der Jagt
- Department of Applied Physics, Eindhoven University of Technology, 5612 AZ, Eindhoven, The Netherlands
| | - Gary W Paterson
- SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Henk J M Swagten
- Department of Applied Physics, Eindhoven University of Technology, 5612 AZ, Eindhoven, The Netherlands
| | - Damien McGrouther
- SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
| |
Collapse
|
54
|
Lo Conte R, Nandy AK, Chen G, Fernandes Cauduro AL, Maity A, Ophus C, Chen Z, N'Diaye AT, Liu K, Schmid AK, Wiesendanger R. Tuning the Properties of Zero-Field Room Temperature Ferromagnetic Skyrmions by Interlayer Exchange Coupling. NANO LETTERS 2020; 20:4739-4747. [PMID: 32459968 DOI: 10.1021/acs.nanolett.0c00137] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Magnetic materials offer an opportunity to overcome the scalability and energy consumption limits affecting the semiconductor industry. New computational device architectures, such as low-power solid state magnetic logic and memory-in-logic devices, have been proposed which rely on the unique properties of magnetic materials. Magnetic skyrmions, topologically protected quasi-particles, are at the core of many of the newly proposed spintronic devices. Many different materials systems have been shown hosting ferromagnetic skyrmions at room temperature. However, a magnetic field is a key ingredient to stabilize skyrmions, and this is not desirable for applications, due to the poor scalability of active components generating magnetic fields. Here we report the observation of ferromagnetic skyrmions at room temperature and zero magnetic field, stabilized through interlayer exchange coupling (IEC) between a reference magnet and a free magnet. Most importantly, by tuning the strength of the IEC, we are able to tune the skyrmion size and areal density. Our findings are relevant to the development of skyrmion-based spintronic devices suitable for general-use applications which go beyond modern nanoelectronics.
Collapse
Affiliation(s)
- Roberto Lo Conte
- Department of Materials Science and Engineering, University of California, Berkeley, California 94720, United States
- Department of Physics, University of Hamburg, D-20355 Hamburg, Germany
| | - Ashis K Nandy
- School of Physical Sciences, National Institute of Science Education and Research, HBNI, P.O. Jatni, 752050, Jatni, India
| | - Gong Chen
- Department of Physics, University of California, Davis, California 95616, United States
| | - Andre L Fernandes Cauduro
- National Center for Electron Microscopy, Molecular Foundry - Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Ajanta Maity
- School of Physical Sciences, National Institute of Science Education and Research, HBNI, P.O. Jatni, 752050, Jatni, India
| | - Colin Ophus
- National Center for Electron Microscopy, Molecular Foundry - Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Zhijie Chen
- Physics Department, Georgetown University, Washington, DC 20057, United States
| | - Alpha T N'Diaye
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Kai Liu
- Department of Physics, University of California, Davis, California 95616, United States
- Physics Department, Georgetown University, Washington, DC 20057, United States
| | - Andreas K Schmid
- National Center for Electron Microscopy, Molecular Foundry - Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | | |
Collapse
|
55
|
Ma T, Sharma AK, Saha R, Srivastava AK, Werner P, Vir P, Kumar V, Felser C, Parkin SSP. Tunable Magnetic Antiskyrmion Size and Helical Period from Nanometers to Micrometers in a D 2d Heusler Compound. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e2002043. [PMID: 32484269 DOI: 10.1002/adma.202002043] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Revised: 04/27/2020] [Indexed: 06/11/2023]
Abstract
Skyrmions and antiskyrmions are magnetic nano-objects with distinct chiral, noncollinear spin textures that are found in various magnetic systems with crystal symmetries that give rise to specific Dzyaloshinskii-Moriya exchange vectors. These magnetic nano-objects are associated with closely related helical spin textures that can form in the same material. The skyrmion size and the period of the helix are generally considered as being determined, in large part, by the ratio of the magnitude of the Heisenberg to that of the Dzyaloshinskii-Moriya exchange interaction. In this work, it is shown by real-space magnetic imaging that the helix period λ and the size of the antiskyrmion daSk in the D2d compound Mn1.4 PtSn can be systematically tuned by more than an order of magnitude from ≈100 nm to more than 1.1 µm by varying the thickness of the lamella in which they are observed. The chiral spin texture is verified to be preserved even up to micrometer-thick layers. This extreme size tunability is shown to arise from long-range magnetodipolar interactions, which typically play a much less important role for B20 skyrmions. This tunability in size makes antiskyrmions very attractive for technological applications.
Collapse
Affiliation(s)
- Tianping Ma
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale), D-06120, Germany
- Institute of Physics, Martin Luther University, Halle-Wittenberg, Halle (Saale), D-06120, Germany
| | - Ankit K Sharma
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale), D-06120, Germany
- Institute of Physics, Martin Luther University, Halle-Wittenberg, Halle (Saale), D-06120, Germany
| | - Rana Saha
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale), D-06120, Germany
| | - Abhay K Srivastava
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale), D-06120, Germany
- Institute of Physics, Martin Luther University, Halle-Wittenberg, Halle (Saale), D-06120, Germany
| | - Peter Werner
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale), D-06120, Germany
| | - Praveen Vir
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straβe 40, Dresden, 01187, Germany
| | - Vivek Kumar
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straβe 40, Dresden, 01187, Germany
| | - Claudia Felser
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straβe 40, Dresden, 01187, Germany
| | - Stuart S P Parkin
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale), D-06120, Germany
- Institute of Physics, Martin Luther University, Halle-Wittenberg, Halle (Saale), D-06120, Germany
| |
Collapse
|
56
|
Hoffmann M, Müller GP, Blügel S. Atomistic Perspective of Long Lifetimes of Small Skyrmions at Room Temperature. PHYSICAL REVIEW LETTERS 2020; 124:247201. [PMID: 32639835 DOI: 10.1103/physrevlett.124.247201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Accepted: 04/20/2020] [Indexed: 06/11/2023]
Abstract
The current development to employ magnetic skyrmions in novel spintronic device designs has led to a demand for room-temperature-stable skyrmions of ever smaller size. We present extensive studies on skyrmion stability in atomistic magnetic systems in two- and three-dimensional geometries. We show that for materials described by the same micromagnetic parameters, the variation of the atomistic exchange between different neighbors, the stacking order, and the number of layers of the atomic lattice can significantly influence the rate of the thermally activated decay of a skyrmion. These factors alone are important considerations, but we show that their combination can open up novel avenues of materials design in the search for sub-10 nm skyrmions, as their lifetime can be extended by several orders of magnitude.
Collapse
Affiliation(s)
- Markus Hoffmann
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Gideon P Müller
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| | - Stefan Blügel
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany
| |
Collapse
|
57
|
Lee AJ, Guo S, Flores J, Wang B, Bagués N, McComb DW, Yang F. Investigation of the Role of Rare-Earth Elements in Spin-Hall Topological Hall Effect in Pt/Ferrimagnetic-Garnet Bilayers. NANO LETTERS 2020; 20:4667-4672. [PMID: 32459494 DOI: 10.1021/acs.nanolett.0c01620] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Topological magnetic textures such as skyrmions are being extensively studied for their potential application in spintronic devices. Recently, low-damping ferrimagnetic insulators (FMI) such as Tm3Fe5O12 have attracted significant interest as potential candidates for hosting skyrmions. Here, we report the detection of the spin-Hall topological Hall effect (SH-THE) in Pt/Tm3Fe5O12 and Pt/Y3Fe5O12 bilayers grown on various orientations of Gd3Ga5O12 substrates as well as on epitaxial buffer layers of Y3Sc2Al3O12, which separates the FMI from the substrate without sacrificing the crystal quality. The presence of SH-THE in all of the bilayers and trilayers provides evidence that rare-earth ions in either the FMI or substrate may not be critical for inducing an interfacial Dzyaloshinskii-Moriya interaction that is necessary to stabilize magnetic textures. Additionally, the use of substrates with various crystal orientations alters the magnetic anisotropy, which shifts the temperatures and strength of the SH-THE.
Collapse
Affiliation(s)
- Aidan J Lee
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Side Guo
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Jose Flores
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| | - Binbin Wang
- Center for Electron Microscopy and Analysis, The Ohio State University, Columbus, Ohio 43210, United States
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, United States
| | - Núria Bagués
- Center for Electron Microscopy and Analysis, The Ohio State University, Columbus, Ohio 43210, United States
| | - David W McComb
- Center for Electron Microscopy and Analysis, The Ohio State University, Columbus, Ohio 43210, United States
- Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210, United States
| | - Fengyuan Yang
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, United States
| |
Collapse
|
58
|
Olleros-Rodríguez P, Guerrero R, Camarero J, Chubykalo-Fesenko O, Perna P. Intrinsic Mixed Bloch-Néel Character and Chirality of Skyrmions in Asymmetric Epitaxial Trilayers. ACS APPLIED MATERIALS & INTERFACES 2020; 12:25419-25427. [PMID: 32401480 DOI: 10.1021/acsami.0c04661] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Recent advances in the stabilization and manipulation of chiral magnetization configurations in systems consisting of alternating atomic layers of ferromagnetic and nonmagnetic materials hold promise for innovation in spintronics technology. The low dimensionality of the systems promotes spin orbit driven interfacial effects like antisymmetric Dzyaloshinskii-Moriya interactions (DMI) and surface magnetic anisotropy, whose relative strengths may be tuned to achieve stable nanometer sized magnetic objects with fixed chirality. While in most of the cases this is obtained by engineering complex multilayers stacks in which interlayer dipolar fields become important, we consider here a simple epitaxial trilayer in which a ferromagnet, with variable thickness, is embedded between a heavy metal and graphene. The latter enhances the perpendicular magnetic anisotropy of the system, promotes a Rashba-type DMI, and can sustain very long spin diffusion lengths. We use a layer-resolved micromagnetic model to describe the magnetization textures and their chirality. Our results demonstrate that for Co thicknesses larger than 3.6 nm, a skyrmion having an intrinsic mixed Bloch-Néel character is stabilized in the entire (single) Co layer.
Collapse
Affiliation(s)
| | - Ruben Guerrero
- IMDEA Nanociencia, c/Faraday 9, Campus de Cantoblanco, 28049 Madrid, Spain
| | - Julio Camarero
- IMDEA Nanociencia, c/Faraday 9, Campus de Cantoblanco, 28049 Madrid, Spain
- Departamento de Física de la Materia Condensada, Instituto "Nicolas Cabrera" and Condensed Matter Physics Center (IFIMAC), Universidad Autonoma de Madrid, Campus de Cantoblanco, 28049 Madrid, Spain
| | | | - Paolo Perna
- IMDEA Nanociencia, c/Faraday 9, Campus de Cantoblanco, 28049 Madrid, Spain
| |
Collapse
|
59
|
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.
Collapse
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
| |
Collapse
|
60
|
Quessab Y, Xu JW, Ma CT, Zhou W, Riley GA, Shaw JM, Nembach HT, Poon SJ, Kent AD. Tuning interfacial Dzyaloshinskii-Moriya interactions in thin amorphous ferrimagnetic alloys. Sci Rep 2020; 10:7447. [PMID: 32366864 PMCID: PMC7198596 DOI: 10.1038/s41598-020-64427-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Accepted: 04/15/2020] [Indexed: 11/26/2022] Open
Abstract
Skyrmions can be stabilized in magnetic systems with broken inversion symmetry and chiral interactions, such as Dzyaloshinskii-Moriya interactions (DMI). Further, compensation of magnetic moments in ferrimagnetic materials can significantly reduce magnetic dipolar interactions, which tend to favor large skyrmions. Tuning DMI is essential to control skyrmion properties, with symmetry breaking at interfaces offering the greatest flexibility. However, in contrast to the ferromagnet case, few studies have investigated interfacial DMI in ferrimagnets. Here we present a systematic study of DMI in ferrimagnetic CoGd films by Brillouin light scattering. We demonstrate the ability to control DMI by the CoGd cap layer composition, the stack symmetry and the ferrimagnetic layer thickness. The DMI thickness dependence confirms its interfacial nature. In addition, magnetic force microscopy reveals the ability to tune DMI in a range that stabilizes sub-100 nm skyrmions at room temperature in zero field. Our work opens new paths for controlling interfacial DMI in ferrimagnets to nucleate and manipulate skyrmions.
Collapse
Affiliation(s)
- Y Quessab
- Center for Quantum Phenomena, Department of Physics, New York University, New York, New York, 10003, USA.
| | - J-W Xu
- Center for Quantum Phenomena, Department of Physics, New York University, New York, New York, 10003, USA
| | - C T Ma
- Department of Physics, University of Virginia, Charlottesville, Virginia, 22904, USA
| | - W Zhou
- Department of Physics, University of Virginia, Charlottesville, Virginia, 22904, USA
| | - G A Riley
- Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado, 80305, USA
- Center for Memory and Recording Research, University of California San Diego, La Jolla, California, 92093, USA
| | - J M Shaw
- Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado, 80305, USA
| | - H T Nembach
- Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado, 80305, USA
- JILA, University of Colorado, Boulder, Colorado, 80309, USA
| | - S J Poon
- Department of Physics, University of Virginia, Charlottesville, Virginia, 22904, USA
| | - A D Kent
- Center for Quantum Phenomena, Department of Physics, New York University, New York, New York, 10003, USA
| |
Collapse
|
61
|
Castro MA, Mancilla-Almonacid D, Valdivia JA, Allende S. Magnetostatic interaction between two bubble skyrmions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:175801. [PMID: 31931481 DOI: 10.1088/1361-648x/ab6aec] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
A detailed analytic and numerical analysis of the interaction between two bubble skyrmions has been carried out. The results from the micromagnetic calculations show that when the skyrmions are in the same plane, the magnetic parameters vary weakly as a function of the separation between them. On the other hand, when the skyrmions are located in the same vertical axis, the magnetic parameters show a strong variation as a function of the separation of the skyrmions. In particular, when a magnetic disk is over another, there is a transition from a Bloch-like skyrmion configuration to a Néel-like skyrmion configuration as the distance between the disks decreases, as a consequence of the magnetostatic interaction. Therefore, it is possible to stabilize a bubble skyrmion with a Néel configuration without the Dzyaloshinskii-Moriya interaction. Thus, these results can be used for the control of the skyrmion parameters in magnetic spintronic devices that need to use these configurations.
Collapse
Affiliation(s)
- M A Castro
- Departamento de Física, CEDENNA, Universidad de Santiago de Chile, USACH, Av. Ecuador 3493, Santiago, Chile
| | | | | | | |
Collapse
|
62
|
Je SG, Han HS, Kim SK, Montoya SA, Chao W, Hong IS, Fullerton EE, Lee KS, Lee KJ, Im MY, Hong JI. Direct Demonstration of Topological Stability of Magnetic Skyrmions via Topology Manipulation. ACS NANO 2020; 14:3251-3258. [PMID: 32129978 DOI: 10.1021/acsnano.9b08699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Topological protection precludes a continuous deformation between topologically inequivalent configurations in a continuum. Motivated by this concept, magnetic skyrmions, topologically nontrivial spin textures, are expected to exhibit topological stability, thereby offering a prospect as a nanometer-scale nonvolatile information carrier. In real materials, however, atomic spins are configured as not continuous but discrete distributions, which raises a fundamental question if the topological stability is indeed preserved for real magnetic skyrmions. Answering this question necessitates a direct comparison between topologically nontrivial and trivial spin textures, but the direct comparison in one sample under the same magnetic fields has been challenging. Here we report how to selectively achieve either a skyrmion state or a topologically trivial bubble state in a single specimen and thereby experimentally show how robust the skyrmion structure is in comparison with the bubbles. We demonstrate that topologically nontrivial magnetic skyrmions show longer lifetimes than trivial bubble structures, evidencing the topological stability in a real discrete system. Our work corroborates the physical importance of the topology in the magnetic materials, which has hitherto been suggested by mathematical arguments, providing an important step toward ever-dense and more-stable magnetic devices.
Collapse
Affiliation(s)
- Soong-Geun Je
- Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department of Emerging Materials Science, DGIST, Daegu 42988, Korea
- Center for Spin-Orbitronic Materials, Korea University, Seoul 02841, Korea
- Department of Physics, Chonnam National University, Gwangju 61186, Korea
| | - Hee-Sung Han
- School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Korea
| | - Se Kwon Kim
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, United States
| | - Sergio A Montoya
- Space and Naval Warfare Systems Center Pacific, San Diego, California 92152, United States
| | - Weilun Chao
- Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Ik-Sun Hong
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, Korea
| | - Eric E Fullerton
- Center for Memory and Recording Research, University of California-San Diego, La Jolla, California 92093, United States
- Department of Electrical and Computer Engineering, University of California-San Diego, La Jolla, California 92093, United States
| | - Ki-Suk Lee
- School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Korea
| | - Kyung-Jin Lee
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, Korea
- Department of Materials Science and Engineering, Korea University, Seoul 02841, Korea
| | - Mi-Young Im
- Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department of Emerging Materials Science, DGIST, Daegu 42988, Korea
- School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Korea
| | - Jung-Il Hong
- Department of Emerging Materials Science, DGIST, Daegu 42988, Korea
| |
Collapse
|
63
|
Yu Z, Shen M, Zeng Z, Liang S, Liu Y, Chen M, Zhang Z, Lu Z, You L, Yang X, Zhang Y, Xiong R. Voltage-controlled skyrmion-based nanodevices for neuromorphic computing using a synthetic antiferromagnet. NANOSCALE ADVANCES 2020; 2:1309-1317. [PMID: 36133072 PMCID: PMC9419653 DOI: 10.1039/d0na00009d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Accepted: 02/06/2020] [Indexed: 06/13/2023]
Abstract
Spintronics exhibits significant potential for a neuromorphic computing system with high speed, high integration density, and low dissipation. In this article, we propose an ultralow-dissipation skyrmion-based nanodevice composed of a synthetic antiferromagnet (SAF) and a piezoelectric substrate for neuromorphic computing. Skyrmions/skyrmion bubbles can be generated in the upper layer of an SAF with a weak anisotropy energy (E a). Applying a weak electric field on the heterostructure, interlayer antiferromagnetic coupling can be manipulated, giving rise to a continuous transition between a large skyrmion bubble and a small skyrmion. This thus induces a variation of the resistance of a magnetic tunneling junction that can mimic the potentiation/depression of a synapse and the leaky-integral-and-fire function of a neuron at a cost of a very low energy consumption of 0.3 fJ. These results pave a way to ultralow power neuromorphic computing applications.
Collapse
Affiliation(s)
- Ziyang Yu
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University Wuhan 430072 P. R. China
| | - Maokang Shen
- School of Optical and Electronic Information, Huazhong University of Science and Technology Wuhan 430074 P. R. China
| | - Zhongming Zeng
- Key Laboratory of Multifunctional Nanomaterials and Smart Systems, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences Suzhou Jiangsu 215123 P. R. China
| | - Shiheng Liang
- Department of Physics, Hubei University Wuhan 430062 P. R. China
| | - Yong Liu
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University Wuhan 430072 P. R. China
| | - Ming Chen
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University Wuhan 430072 P. R. China
| | - Zhenhua Zhang
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University Wuhan 430072 P. R. China
| | - Zhihong Lu
- The State Key Laboratory of Refractories and Metallurgy, School of Materials and Metallurgy, Wuhan University of Science and Technology Wuhan 430081 P. R. China
| | - Long You
- School of Optical and Electronic Information, Huazhong University of Science and Technology Wuhan 430074 P. R. China
| | - Xiaofei Yang
- School of Optical and Electronic Information, Huazhong University of Science and Technology Wuhan 430074 P. R. China
| | - Yue Zhang
- School of Optical and Electronic Information, Huazhong University of Science and Technology Wuhan 430074 P. R. China
| | - Rui Xiong
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University Wuhan 430072 P. R. China
| |
Collapse
|
64
|
Pöllath S, Lin T, Lei N, Zhao W, Zweck J, Back CH. Spin structure relation to phase contrast imaging of isolated magnetic Bloch and Néel skyrmions. Ultramicroscopy 2020; 212:112973. [PMID: 32151794 DOI: 10.1016/j.ultramic.2020.112973] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Revised: 02/19/2020] [Accepted: 02/26/2020] [Indexed: 11/17/2022]
Abstract
Magnetic skyrmions are promising candidates for future storage devices with a large data density. A great variety of materials have been found that host skyrmions up to the room-temperature regime. Lorentz microscopy, usually performed in a transmission electron microscope (TEM), is one of the most important tools for characterizing skyrmion samples in real space. Using numerical calculations, this work relates the phase contrast in a TEM to the actual magnetization profile of an isolated Néel or Bloch skyrmion, the two most common skyrmion types. Within the framework of the used skyrmion model, the results are independent of skyrmion size and wall width and scale with sample thickness for purely magnetic specimens. Simple rules are provided to extract the actual skyrmion configuration of pure Bloch or Néel skyrmions without the need of simulations. Furthermore, first differential phase contrast (DPC) measurements on Néel skyrmions that meet experimental expectations are presented and showcase the described principles. The work is relevant for material sciences where it enables the engineering of skyrmion profiles via convenient characterization.
Collapse
Affiliation(s)
- S Pöllath
- Institut für Experimentelle Physik, Universität Regensburg, Regensburg D-93040, Germany
| | - T Lin
- Fert Beijing Institute, BDBC, School of Microelectronics, Beihang University, Beijing 100191, China
| | - N Lei
- Fert Beijing Institute, BDBC, School of Microelectronics, Beihang University, Beijing 100191, China
| | - W Zhao
- Fert Beijing Institute, BDBC, School of Microelectronics, Beihang University, Beijing 100191, China
| | - J Zweck
- Institut für Experimentelle Physik, Universität Regensburg, Regensburg D-93040, Germany
| | - C H Back
- Physik-Department, Technische Universität München, Garching D-85748, Germany; Munich Center for Quantum Science and Technology (MCQST), Schellingstr. 4, München D-80799, Germany.
| |
Collapse
|
65
|
Legrand W, Maccariello D, Ajejas F, Collin S, Vecchiola A, Bouzehouane K, Reyren N, Cros V, Fert A. Room-temperature stabilization of antiferromagnetic skyrmions in synthetic antiferromagnets. NATURE MATERIALS 2020; 19:34-42. [PMID: 31477905 DOI: 10.1038/s41563-019-0468-3] [Citation(s) in RCA: 80] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2018] [Accepted: 07/24/2019] [Indexed: 05/23/2023]
Abstract
Room-temperature skyrmions in ferromagnetic films and multilayers show promise for encoding information bits in new computing technologies. Despite recent progress, ferromagnetic order generates dipolar fields that prevent ultrasmall skyrmion sizes, and allows a transverse deflection of moving skyrmions that hinders their efficient manipulation. Antiferromagnetic skyrmions shall lift these limitations. Here we demonstrate that room-temperature antiferromagnetic skyrmions can be stabilized in synthetic antiferromagnets (SAFs), in which perpendicular magnetic anisotropy, antiferromagnetic coupling and chiral order can be adjusted concurrently. Utilizing interlayer electronic coupling to an adjacent bias layer, we demonstrate that spin-spiral states obtained in a SAF with vanishing perpendicular magnetic anisotropy can be turned into isolated antiferromagnetic skyrmions. We also provide model-based estimates of skyrmion size and stability, showing that room-temperature antiferromagnetic skyrmions below 10 nm in radius can be anticipated in further optimized SAFs. Antiferromagnetic skyrmions in SAFs may thus solve major issues associated with ferromagnetic skyrmions for low-power spintronic devices.
Collapse
Affiliation(s)
- William Legrand
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France.
| | - Davide Maccariello
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France
| | - Fernando Ajejas
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France
| | - Sophie Collin
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France
| | - Aymeric Vecchiola
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France
| | - Karim Bouzehouane
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France
| | - Nicolas Reyren
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France
| | - Vincent Cros
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France.
| | - Albert Fert
- Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau, France
| |
Collapse
|
66
|
Bornemann M, Grytsiuk S, Baumeister PF, Dos Santos Dias M, Zeller R, Lounis S, Blügel S. Complex magnetism of B20-MnGe: from spin-spirals, hedgehogs to monopoles. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:485801. [PMID: 31382246 DOI: 10.1088/1361-648x/ab38a0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
B20 compounds are the playground for various non-trivial magnetic textures such as skyrmions, which are topologically protected states. Recent measurements on B20-MnGe indicate no clear consensus on its magnetic behavior, which is characterized by the presence of either spin-spirals or three-dimensional objects interpreted to be a cubic lattice of hedgehogs and anti-hedgehogs. Utilizing a massively parallel linear scaling all-electron density functional algorithm, we find from full first-principles simulations on cells containing thousands of atoms that upon increase of the compound volume, the state with lowest energy switches across different magnetic phases: ferromagnetic, spin-spiral, hedgehog and monopole.
Collapse
Affiliation(s)
- Marcel Bornemann
- Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich & JARA, 52425 Jülich, Germany
| | | | | | | | | | | | | |
Collapse
|
67
|
Stavrou VD, Kourounis D, Dimakopoulos K, Panagiotopoulos I, Gergidis LN. Magnetic skyrmions in FePt nanoparticles having Reuleaux 3D geometry: a micromagnetic simulation study. NANOSCALE 2019; 11:20102-20114. [PMID: 31612890 DOI: 10.1039/c9nr04829d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The magnetization reversal in magnetic FePt nanoelements having Reuleaux 3D geometry is studied using micromagnetic simulations employing Finite Element discretizations. Magnetic skyrmions are revealed in different systems generated by the variation of the magnitude of the magnetocrystalline anisotropy which was kept normal to the nanoelement's base and parallel to the applied external field. The topological quantity of skyrmion number is computed in order to characterize micromagnetic configurations exhibiting skyrmionic formations. Micromagnetic configurations with a wide range of skyrmion numbers between -3 and 3 are indicative for the existence of one or multiple skyrmions that have been detected and stabilized in a range of external fields. Internal magnetic structures are shown consisting of Bloch type skyrmionic entities in the bulk altered to Néel skyrmions on the nanoelement's bottom and top base surfaces. The actual sizes of the formed skyrmions and the internal magnetization structures were computed. In particular, the sizes of the generated and persistent skyrmions were calculated as functions of the magnetocrystalline anisotropy value and of the applied external magnetic field. It is shown that the size of skyrmions is linearly dependent on the external field value. The slope of the linear curve can be controlled by the magnetocrystalline anisotropy value. The magnetic skyrmions can be created for FePt magnetic systems lacking of chiral interactions by designing the geometry-shape of the nanoparticle and by controlling the value of magnetocrystalline anisotropy.
Collapse
Affiliation(s)
- Vasileios D Stavrou
- Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina, Greece.
| | | | | | - Ioannis Panagiotopoulos
- Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina, Greece.
| | - Leonidas N Gergidis
- Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina, Greece.
| |
Collapse
|
68
|
Formation and current-induced motion of synthetic antiferromagnetic skyrmion bubbles. Nat Commun 2019; 10:5153. [PMID: 31727895 PMCID: PMC6856122 DOI: 10.1038/s41467-019-13182-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Accepted: 10/25/2019] [Indexed: 11/08/2022] Open
Abstract
Skyrmion, a topologically-protected soliton, is known to emerge via electron spin in various magnetic materials. The magnetic skyrmion can be driven by low current density and has a potential to be stabilized in nanoscale, offering new directions of spintronics. However, there remain some fundamental issues in widely-studied ferromagnetic systems, which include a difficulty to realize stable ultrasmall skyrmions at room temperature, presence of the skyrmion Hall effect, and limitation of velocity owing to the topological charge. Here we show skyrmion bubbles in a synthetic antiferromagnetic coupled multilayer that are free from the above issues. Additive Dzyaloshinskii-Moriya interaction and spin-orbit torque (SOT) of the tailored stack allow stable skyrmion bubbles at room temperature, significantly smaller threshold current density or higher speed for motion, and negligible skyrmion Hall effect, with a potential to be scaled down to nanometer dimensions. The results offer a promising pathway toward nanoscale and energy-efficient skyrmion-based devices.
Collapse
|
69
|
Zivieri R. Statistical Thermodynamics of Chiral Skyrmions in a Ferromagnetic Material. MATERIALS 2019; 12:ma12223702. [PMID: 31717604 PMCID: PMC6888473 DOI: 10.3390/ma12223702] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Revised: 11/04/2019] [Accepted: 11/06/2019] [Indexed: 12/01/2022]
Abstract
Solitons are a challenging topic in condensed matter physics and materials science because of the interplay between their topological and physical properties and for the crucial role they play in topological phase transitions. Among them, chiral skyrmions hosted in ferromagnetic systems are axisymmetric solitonic states attracting a lot of attention for their dazzling physical properties and technological applications. In this paper, the equilibrium statistical thermodynamics of chiral magnetic skyrmions developing in a ferromagnetic material having the shape of an ultrathin cylindrical dot is investigated. This is accomplished by determining via analytical calculations for both Néel and Bloch skyrmions: (1) the internal energy of a single chiral skyrmion; (2) the partition function; (3) the free energy; (4) the pressure; and (5) the equation of state of a skyrmion diameters population. To calculate the thermodynamic functions for points (2)–(5), the derivation of the average internal energy and of the configurational entropy is crucial. Numerical calculations of the thermodynamic functions for points (1)–(5) are applied to Néel skyrmions. These results could advance the field of materials science with special regard to low-dimensional magnetic systems.
Collapse
Affiliation(s)
- Roberto Zivieri
- Department of Mathematical and Computer Sciences, Physical Sciences and Earth Sciences, University of Messina, Contrada di Dio, 98166 Messina, Italy
| |
Collapse
|
70
|
Isolated zero field sub-10 nm skyrmions in ultrathin Co films. Nat Commun 2019; 10:3823. [PMID: 31444358 PMCID: PMC6707282 DOI: 10.1038/s41467-019-11831-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Accepted: 07/30/2019] [Indexed: 11/08/2022] Open
Abstract
Due to their exceptional topological and dynamical properties magnetic skyrmions—localized stable spin structures—show great promise for spintronic applications. To become technologically competitive, isolated skyrmions with diameters below 10 nm stable at zero magnetic field and at room temperature are desired. Despite finding skyrmions in a wide spectrum of materials, the quest for a material with these envisioned properties is ongoing. Here we report zero field isolated skyrmions at T = 4 K with diameters below 5 nm observed in the virgin ferromagnetic state coexisting with 1 nm thin domain walls in Rh/Co atomic bilayers on Ir(111). These spin structures are investigated by spin-polarized scanning tunneling microscopy and can also be detected using non-spin-polarized tips via the noncollinear magnetoresistance. We demonstrate that sub-10 nm skyrmions are stabilized in these ferromagnetic Co films at zero field due to strong frustration of exchange interaction, together with Dzyaloshinskii–Moriya interaction and large magnetocrystalline anisotropy. Isolated skyrmions with diameters below 10 nm stabilized at zero magnetic field are of great technological relevance to the future spintronic applications. Here the authors report stabilization of zero field isolated skyrmions with diameters smaller than 5 nm in Rh/Co atomic bilayers on the Ir(111) surface.
Collapse
|
71
|
Electrical writing, deleting, reading, and moving of magnetic skyrmioniums in a racetrack device. Sci Rep 2019; 9:12119. [PMID: 31431688 PMCID: PMC6702348 DOI: 10.1038/s41598-019-48617-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Accepted: 08/07/2019] [Indexed: 11/23/2022] Open
Abstract
A magnetic skyrmionium (also called 2π-skyrmion) can be understood as a skyrmion—a topologically nontrivial magnetic whirl—which is situated in the center of a second skyrmion with reversed magnetization. Here, we propose a new optoelectrical writing and deleting mechanism for skyrmioniums in thin films, as well as a reading mechanism based on the topological Hall voltage. Furthermore, we point out advantages for utilizing skyrmioniums as carriers of information in comparison to skyrmions with respect to the current-driven motion. We simulate all four constituents of an operating skyrmionium-based racetrack storage device: creation, motion, detection and deletion of bits. The existence of a skyrmionium is thereby interpreted as a ‘1’ and its absence as a ‘0’ bit.
Collapse
|
72
|
Robust Formation of Ultrasmall Room-Temperature Neél Skyrmions in Amorphous Ferrimagnets from Atomistic Simulations. Sci Rep 2019; 9:9964. [PMID: 31292514 PMCID: PMC6620327 DOI: 10.1038/s41598-019-46458-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Accepted: 06/28/2019] [Indexed: 11/10/2022] Open
Abstract
Neél skyrmions originate from interfacial Dzyaloshinskii Moriya interaction (DMI). Recent studies have explored using thin-film ferromagnets and ferrimagnets to host Neél skyrmions for spintronic applications. However, it is unclear if ultrasmall (10 nm or less) skyrmions can ever be stabilized at room temperature for practical use in high density parallel racetrack memories. While thicker films can improve stability, DMI decays rapidly away from the interface. As such, spins far away from the interface would experience near-zero DMI, raising question on whether or not unrealistically large DMI is needed to stabilize skyrmions, and whether skyrmions will also collapse away from the interface. To address these questions, we have employed atomistic stochastic Landau-Lifshitz-Gilbert simulations to investigate skyrmions in amorphous ferrimagnetic GdCo. It is revealed that a significant reduction in DMI below that of Pt is sufficient to stabilize ultrasmall skyrmions even in films as thick as 15 nm. Moreover, skyrmions are found to retain a uniform columnar shape across the film thickness due to the long ferrimagnetic exchange length despite the decaying DMI. Our results show that increasing thickness and reducing DMI in GdCo can further reduce the size of skyrmions at room temperature, which is crucial to improve the density and energy efficiency in skyrmion based devices.
Collapse
|
73
|
Göbel B, Henk J, Mertig I. Forming individual magnetic biskyrmions by merging two skyrmions in a centrosymmetric nanodisk. Sci Rep 2019; 9:9521. [PMID: 31266991 PMCID: PMC6606756 DOI: 10.1038/s41598-019-45965-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Accepted: 06/17/2019] [Indexed: 11/25/2022] Open
Abstract
When two magnetic skyrmions - whirl-like, topologically protected quasiparticles - form a bound pair, a biskyrmion state with a topological charge of NSk = ±2 is constituted. Recently, especially the case of two partially overlapping skyrmions has brought about great research interest. Since for its formation the individual skyrmions need to posses opposite in-plane magnetizations, such a biskyrmion cannot be stabilized by the Dzyaloshinskii-Moriya-interaction (DMI), which is the interaction that typically stabilizes skyrmions in non-centrosymmetric materials and at interfaces. Here, we show that these biskyrmions can be stabilized by the dipole-dipole interaction in centrosymmetric materials in which the DMI is forbidden. Analytical considerations indicate that the bound state of a biskyrmion is energetically preferable over two individual skyrmions. As a result, when starting from two skyrmions in a micromagnetic simulation, a biskyrmion is formed upon relaxation. We propose a scheme that allows to control this biskyrmion formation in nanodisks and analyze the individual steps.
Collapse
Affiliation(s)
- Börge Göbel
- Max-Planck-Institut für Mikrostrukturphysik, Halle (Saale), 06120, Germany.
| | - Jürgen Henk
- Martin-Luther-Universität Halle-Wittenberg, Institut für Physik, Halle (Saale), 06099, Germany
| | - Ingrid Mertig
- Max-Planck-Institut für Mikrostrukturphysik, Halle (Saale), 06120, Germany
- Martin-Luther-Universität Halle-Wittenberg, Institut für Physik, Halle (Saale), 06099, Germany
| |
Collapse
|
74
|
Direct current-tunable MHz to multi-GHz skyrmion generation and control. Sci Rep 2019; 9:9496. [PMID: 31263133 PMCID: PMC6603187 DOI: 10.1038/s41598-019-45972-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Accepted: 06/18/2019] [Indexed: 11/08/2022] Open
Abstract
Skyrmions offer high density, low power, and nonvolatile memory functionalities due to their nanoscale and topologically-protected chiral spin structures. For integrated high-bandwidth devices, one needs to control skyrmion generation and propagation rates using current. Here, we introduce a skyrmion initialization and control method to generate periodic skyrmions from 114 MHz to 21 GHz using spin-polarized direct current. We first initialize a stable magnetic domain profile that is pinned between a notch and a rectangular constriction using a DC pulse. Next, we pass spin-polarized DC charge current to eject periodic skyrmions at a desired frequency. By changing the DC current density, we demonstrate in micromagnetic simulations that skyrmion generation frequencies can be controlled reversibly over more than seven octaves of frequencies. By using domain pinning and current-driven skyrmion motion, we demonstrate a highly tunable and DC-controlled skyrmion signal source, which pave the way towards ultra wideband, compact and integrated skyrmionic circuits.
Collapse
|
75
|
Dynamics of skyrmion in disordered chiral magnet of thin film form. Sci Rep 2019; 9:5111. [PMID: 30911022 PMCID: PMC6434043 DOI: 10.1038/s41598-019-41441-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Accepted: 03/05/2019] [Indexed: 11/16/2022] Open
Abstract
Magnetic skyrmion is a topological spin texture characterized by the mapping from the two dimensional real space to the unit sphere. It is realized in chiral magnets under an external magnetic field in the plane perpendicular to it. In thin film samples, which are most relevant to the applications, the thickness of the system parallel to the magnetic field is finite, and a skyrmion turns into a skyrmion string, which is often assumed to be a straight rod. There are phenomena related to the internal degrees of freedom along the string, e.g., the monopole and anti-monopole creation/annihilation, corresponding to the change in the skyrmion number. However, the role of this finite thickness in the topological stability and dynamics has not been explored yet. Here we study theoretically the current-driven dynamics of a skyrmion string under disorder potential by systematically changing the thickness of the sample to reveal the dynamical phase diagram in the plane of current density and thickness. We found the three regions, i.e., (i) pinned skyrmion string, (ii) moving depinned skyrmion string, and (iii) annihilation of skyrmion string, for thin and thick limits while (iii) is missing in the intermediate case. This indicates that there is the optimal range of thickness for the topological stability of skyrmion string enhanced compared with a two-dimensional skyrmion. This result provides a way to design and control skyrmions in thin films and interfaces of finite thickness.
Collapse
|
76
|
Abstract
The next-generation logic and memory devices using magnetic skyrmions as spintronic information carriers are frequently studied, thanks to their remarkable magnetic stability, extremely compact size and very-low-cost driving forces within nanotracks. In order to realize skyrmion-based spintronic devices, understanding the skyrmion generation and their dynamics are essential. In this study, we have carried out a systematic micromagnetic simulation study on coherent magnetic skyrmion generation in which we theoretically engineered nanotracks by embedding an anti-notch to a channel of certain width. We found that the drift velocity and the skyrmion generation frequency can be tailored by the applied spin-polarized DC current density. Moreover, skyrmion generation is crucially affected by both damping and nonadiabaticity parameters, as well as the geometry of the anti-notch. We anticipate that our predictions provide rational basis for skyrmion-based devices in which skyrmions are used as information carriers, and influence future discussions.
Collapse
|
77
|
First-Principles Prediction of Skyrmionic Phase Behavior in GdFe2 Films Capped by 4d and 5d Transition Metals. APPLIED SCIENCES-BASEL 2019. [DOI: 10.3390/app9040630] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In atomic GdFe 2 films capped by 4d and 5d transition metals, we show that skyrmions with diameters smaller than 12 nm can emerge. The Dzyaloshinskii–Moriya interaction (DMI), exchange energy, and the magnetocrystalline anisotropy (MCA) energy were investigated based on density functional theory. Since DMI and MCA are caused by spin–orbit coupling (SOC), they are increased with 5d capping layers which exhibit strong SOC strength. We discover a skyrmion phase by using atomistic spin dynamic simulations at small magnetic fields of ∼1 T. In addition, a ground state that a spin spiral phase is remained even at zero magnetic field for both films with 4d and 5d capping layers.
Collapse
|
78
|
Caretta L, Mann M, Büttner F, Ueda K, Pfau B, Günther CM, Hessing P, Churikova A, Klose C, Schneider M, Engel D, Marcus C, Bono D, Bagschik K, Eisebitt S, Beach GSD. Fast current-driven domain walls and small skyrmions in a compensated ferrimagnet. NATURE NANOTECHNOLOGY 2018; 13:1154-1160. [PMID: 30224795 DOI: 10.1038/s41565-018-0255-3] [Citation(s) in RCA: 108] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 08/07/2018] [Indexed: 06/08/2023]
Abstract
Spintronics is a research field that aims to understand and control spins on the nanoscale and should enable next-generation data storage and manipulation. One technological and scientific key challenge is to stabilize small spin textures and to move them efficiently with high velocities. For a long time, research focused on ferromagnetic materials, but ferromagnets show fundamental limits for speed and size. Here, we circumvent these limits using compensated ferrimagnets. Using ferrimagnetic Pt/Gd44Co56/TaOx films with a sizeable Dzyaloshinskii-Moriya interaction, we realize a current-driven domain wall motion with a speed of 1.3 km s-1 near the angular momentum compensation temperature (TA) and room-temperature-stable skyrmions with minimum diameters close to 10 nm near the magnetic compensation temperature (TM). Both the size and dynamics of the ferrimagnet are in excellent agreement with a simplified effective ferromagnet theory. Our work shows that high-speed, high-density spintronics devices based on current-driven spin textures can be realized using materials in which TA and TM are close together.
Collapse
Affiliation(s)
- Lucas Caretta
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Maxwell Mann
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Felix Büttner
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Kohei Ueda
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | | | - Christian M Günther
- Max-Born-Institut, Berlin, Germany
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Berlin, Germany
| | | | - Alexandra Churikova
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | | | | | | | - Colin Marcus
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - David Bono
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Kai Bagschik
- Deutsches Elektronen-Synchrotron (DESY), FS-PE, Hamburg, Germany
| | - Stefan Eisebitt
- Max-Born-Institut, Berlin, Germany
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Berlin, Germany
| | - Geoffrey S D Beach
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
| |
Collapse
|
79
|
Je SG, Vallobra P, Srivastava T, Rojas-Sánchez JC, Pham TH, Hehn M, Malinowski G, Baraduc C, Auffret S, Gaudin G, Mangin S, Béa H, Boulle O. Creation of Magnetic Skyrmion Bubble Lattices by Ultrafast Laser in Ultrathin Films. NANO LETTERS 2018; 18:7362-7371. [PMID: 30295499 DOI: 10.1021/acs.nanolett.8b03653] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Magnetic skyrmions are topologically nontrivial spin textures which hold great promise as stable information carriers in spintronic devices at the nanoscale. One of the major challenges for developing novel skyrmion-based memory and logic devices is fast and controlled creation of magnetic skyrmions at ambient conditions. Here we demonstrate controlled generation of skyrmion bubbles and skyrmion bubble lattices from a ferromagnetic state in sputtered ultrathin magnetic films at room temperature by a single ultrafast (35 fs) laser pulse. The skyrmion bubble density increases with the laser fluence, and it finally becomes saturated, forming disordered hexagonal lattices. Moreover, we present that the skyrmion bubble lattice configuration leads to enhanced topological stability as compared to isolated skyrmions, suggesting its promising use in data storage. Our findings shed light on the optical approach to the skyrmion bubble lattice in commonly accessible materials, paving the road toward the emerging skyrmion-based memory and synaptic devices.
Collapse
Affiliation(s)
- Soong-Geun Je
- INAC-SPINTEC, CNRS, CEA, Grenoble INP , Université Grenoble Alpes , 38000 Grenoble , France
- Institut Jean Lamour, CNRS UMR 7198 , Université de Lorraine , Nancy F-54500 , France
| | - Pierre Vallobra
- Institut Jean Lamour, CNRS UMR 7198 , Université de Lorraine , Nancy F-54500 , France
| | - Titiksha Srivastava
- INAC-SPINTEC, CNRS, CEA, Grenoble INP , Université Grenoble Alpes , 38000 Grenoble , France
| | | | - Thai Ha Pham
- Institut Jean Lamour, CNRS UMR 7198 , Université de Lorraine , Nancy F-54500 , France
| | - Michel Hehn
- Institut Jean Lamour, CNRS UMR 7198 , Université de Lorraine , Nancy F-54500 , France
| | - Gregory Malinowski
- Institut Jean Lamour, CNRS UMR 7198 , Université de Lorraine , Nancy F-54500 , France
| | - Claire Baraduc
- INAC-SPINTEC, CNRS, CEA, Grenoble INP , Université Grenoble Alpes , 38000 Grenoble , France
| | - Stéphane Auffret
- INAC-SPINTEC, CNRS, CEA, Grenoble INP , Université Grenoble Alpes , 38000 Grenoble , France
| | - Gilles Gaudin
- INAC-SPINTEC, CNRS, CEA, Grenoble INP , Université Grenoble Alpes , 38000 Grenoble , France
| | - Stéphane Mangin
- Institut Jean Lamour, CNRS UMR 7198 , Université de Lorraine , Nancy F-54500 , France
| | - Hélène Béa
- INAC-SPINTEC, CNRS, CEA, Grenoble INP , Université Grenoble Alpes , 38000 Grenoble , France
| | - Olivier Boulle
- INAC-SPINTEC, CNRS, CEA, Grenoble INP , Université Grenoble Alpes , 38000 Grenoble , France
| |
Collapse
|
80
|
Aranda AR, Guslienko KY. Single Chiral Skyrmions in Ultrathin Magnetic Films. MATERIALS 2018; 11:ma11112238. [PMID: 30423873 PMCID: PMC6266657 DOI: 10.3390/ma11112238] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Revised: 10/30/2018] [Accepted: 11/07/2018] [Indexed: 11/16/2022]
Abstract
The stability and sizes of chiral skyrmions in ultrathin magnetic films are calculated accounting for the isotropic exchange, Dzyaloshinskii⁻Moriya exchange interaction (DMI), and out-of-plane magnetic anisotropy within micromagnetic approach. Bloch skyrmions in ultrathin magnetic films with B20 cubic crystal structure (MnSi, FeGe) and Neel skyrmions in ultrathin films and multilayers Co/X (X = Ir, Pd, Pt) are considered. The generalized DeBonte ansatz is used to describe the inhomogeneous skyrmion magnetization. The single skyrmion metastability/instability area, skyrmion radius, and skyrmion width are found analytically as a function of DMI strength d . It is shown that the single chiral skyrmions are metastable in infinite magnetic films below a critical value of DMI d c , and do not exist at d > d c . The calculated skyrmion radius increases as d increases and diverges at d → d c - 0 , whereas the skyrmion width increases monotonically as d increases up to d c without any singularities. The calculated skyrmion width is essentially smaller than the one calculated within the generalized domain wall model.
Collapse
Affiliation(s)
- Arantxa R Aranda
- Dpto. Física de Materiales, Universidad del País Vasco, UPV/EHU, 20018 San Sebastián, Spain.
| | - Konstantin Y Guslienko
- Dpto. Física de Materiales, Universidad del País Vasco, UPV/EHU, 20018 San Sebastián, Spain.
- IKERBASQUE, the Basque Foundation for Science, 48013 Bilbao, Spain.
| |
Collapse
|