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Thomsen JD, Han MG, Penn AN, Foucher AC, Geiwitz M, Burch KS, Dekanovsky L, Sofer Z, Liu Y, Petrovic C, Ross FM, Zhu Y, Narang P. Effect of Surface Oxidation and Crystal Thickness on the Magnetic Properties and Magnetic Domain Structures of Cr 2Ge 2Te 6. ACS Nano 2024. [PMID: 38739873 DOI: 10.1021/acsnano.3c09858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
van der Waals (vdW) magnetic materials, such as Cr2Ge2Te6 (CGT), show promise for memory and logic applications. This is due to their broadly tunable magnetic properties and the presence of topological magnetic features such as skyrmionic bubbles. A systematic study of thickness and oxidation effects on magnetic domain structures is important for designing devices and vdW heterostructures for practical applications. Here, we investigate thickness effects on magnetic properties, magnetic domains, and bubbles in oxidation-controlled CGT crystals. We find that CGT exposed to ambient conditions for 5 days forms an oxide layer approximately 5 nm thick. This oxidation leads to a significant increase in the oxidation state of the Cr ions, indicating a change in local magnetic properties. This is supported by real-space magnetic texture imaging through Lorentz transmission electron microscopy. By comparing the thickness-dependent saturation field of oxidized and pristine crystals, we find that oxidation leads to a nonmagnetic surface layer that is thicker than the oxide layer alone. We also find that the stripe domain width and skyrmionic bubble size are strongly affected by the crystal thickness in pristine crystals. These findings underscore the impact of thickness and surface oxidation on the properties of CGT, such as saturation field and domain/skyrmionic bubble size, and suggest a pathway for manipulating magnetic properties through a controlled oxidation process.
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Affiliation(s)
- Joachim Dahl Thomsen
- Division of Physical Sciences, College of Letters and Science, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Myung-Geun Han
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Aubrey N Penn
- MIT.nano, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Alexandre C Foucher
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Michael Geiwitz
- Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, United States
| | - Kenneth Stephen Burch
- Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, United States
| | - Lukas Dekanovsky
- Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Technická 5, Prague 6 166 28, Czech Republic
| | - Zdeněk Sofer
- Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Technická 5, Prague 6 166 28, Czech Republic
| | - Yu Liu
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York 11973, United States
- Center for Correlated Matter and School of Physics, Zhejiang University, Hangzhou 310058, People's Republic of China
| | - Cedomir Petrovic
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York 11973, United States
- Shanghai Key Laboratory of Material Frontiers Research in Extreme Environments (MFree), Shanghai Advanced Research in Physical Sciences (SHARPS), Pudong, Shanghai 201203, People's Republic of China
| | - Frances M Ross
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Yimei Zhu
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Prineha Narang
- Division of Physical Sciences, College of Letters and Science, University of California, Los Angeles, Los Angeles, California 90095, United States
- Electrical and Computer Engineering Department, University of California, Los Angeles, Los Angeles, California 90095, United States
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2
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Liu C, Zhang S, Hao H, Algaidi H, Ma Y, Zhang XX. Magnetic Skyrmions above Room Temperature in a van der Waals Ferromagnet Fe 3GaTe 2. Adv Mater 2024; 36:e2311022. [PMID: 38290153 DOI: 10.1002/adma.202311022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2023] [Revised: 01/11/2024] [Indexed: 02/01/2024]
Abstract
2D van der Waals (vdW) ferromagnetic crystals are a promising platform for innovative spintronic devices based on magnetic skyrmions, thanks to their high flexibility and atomic thickness stability. However, room-temperature skyrmion-hosting vdW materials are scarce, which poses a challenge for practical applications. In this study, a chemical vapor transport (CVT) approach is employed to synthesize Fe3GaTe2 crystals and room-temperature Néel skyrmions are observed in Fe3GaTe2 nanoflakes above 58 nm in thickness through in situ Lorentz transmission electron microscopy (L-TEM). Upon an optimized field cooling procedure, zero-field hexagonal skyrmion lattices are successfully generated in nanoflakes with an extended thickness range (30-180 nm). Significantly, these skyrmion lattices remain stable up to 355 K, setting a new record for the highest temperature at which skyrmions can be hosted. The research establishes Fe3GaTe2 as an emerging above-room-temperature skyrmion-hosting vdW material, holding great promise for future spintronics.
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Affiliation(s)
- Chen Liu
- Physical Science and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
| | - Senfu Zhang
- Physical Science and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
- Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Hongyuan Hao
- Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Hanin Algaidi
- Physical Science and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
| | - Yinchang Ma
- Physical Science and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
| | - Xi-Xiang Zhang
- Physical Science and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
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Yasin FS, Masell J, Takahashi Y, Akashi T, Baba N, Karube K, Shindo D, Arima T, Taguchi Y, Tokura Y, Tanigaki T, Yu X. Bloch Point Quadrupole Constituting Hybrid Topological Strings Revealed with Electron Holographic Vector Field Tomography. Adv Mater 2024; 36:e2311737. [PMID: 38219021 DOI: 10.1002/adma.202311737] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Revised: 12/22/2023] [Indexed: 01/15/2024]
Abstract
Topological magnetic (anti)skyrmions are robust string-like objects heralded as potential components in next-generation topological spintronics devices due to their low-energy manipulability via stimuli such as magnetic fields, heat, and electric/thermal current. While these 2D topological objects are widely studied, intrinsically 3D electron-spin real-space topology remains less explored despite its prevalence in bulky magnets. 2D-imaging studies reveal peculiar vortex-like contrast in the core regions of spin textures present in antiskyrmion-hosting thin plate magnets with S4 crystal symmetry, suggesting a more complex 3D real-space structure than the 2D model suggests. Here, holographic vector field electron tomography captures the 3D structure of antiskyrmions in a single-crystal, precision-doped (Fe0.63Ni0.3Pd0.07)3P (FNPP) lamellae at room temperature and zero field. These measurements reveal hybrid string-like solitons composed of skyrmions with topological number W = -1 on the lamellae's surfaces and an antiskyrmion (W = + 1) connecting them. High-resolution images uncover a Bloch point quadrupole (four magnetic (anti)monopoles that are undetectable in 2D imaging) which enables the observed lengthwise topological transitions. Numerical calculations corroborate the stability of hybrid strings over their conventional (anti)skyrmion counterparts. Hybrid strings result in topological tuning, a tunable topological Hall effect, and the suppression of skyrmion Hall motion, disrupting existing paradigms within spintronics.
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Affiliation(s)
- Fehmi Sami Yasin
- RIKEN Center for Emergent Matter Science (CEMS), RIKEN, Wako, 351-0198, Japan
| | - Jan Masell
- RIKEN Center for Emergent Matter Science (CEMS), RIKEN, Wako, 351-0198, Japan
- Institute of Theoretical Solid State Physics, Karlsruhe Institute of Technology (KIT), 76049, Karlsruhe, Germany
| | - Yoshio Takahashi
- Research and Development Group, Hitachi Ltd., Hatoyama, 350-0395, Japan
| | - Tetsuya Akashi
- Research and Development Group, Hitachi Ltd., Hatoyama, 350-0395, Japan
| | - Norio Baba
- Research Institute for Science and Technology, Kogakuin University, Hachioji, 192-0015, Japan
| | - Kosuke Karube
- RIKEN Center for Emergent Matter Science (CEMS), RIKEN, Wako, 351-0198, Japan
| | - Daisuke Shindo
- RIKEN Center for Emergent Matter Science (CEMS), RIKEN, Wako, 351-0198, Japan
| | - Takahisa Arima
- RIKEN Center for Emergent Matter Science (CEMS), RIKEN, Wako, 351-0198, Japan
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, 277-8561, Japan
| | - Yasujiro Taguchi
- RIKEN Center for Emergent Matter Science (CEMS), RIKEN, Wako, 351-0198, Japan
| | - Yoshinori Tokura
- RIKEN Center for Emergent Matter Science (CEMS), RIKEN, Wako, 351-0198, Japan
- Department of Applied Physics, University of Tokyo, Tokyo, 113-8656, Japan
- Tokyo College, University of Tokyo, Tokyo, 113-8656, Japan
| | - Toshiaki Tanigaki
- Research and Development Group, Hitachi Ltd., Hatoyama, 350-0395, Japan
| | - Xiuzhen Yu
- RIKEN Center for Emergent Matter Science (CEMS), RIKEN, Wako, 351-0198, Japan
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Gopi AK, Srivastava AK, Sharma AK, Chakraborty A, Das S, Deniz H, Ernst A, Hazra BK, Meyerheim HL, Parkin SSP. Thickness-Tunable Zoology of Magnetic Spin Textures Observed in Fe 5GeTe 2. ACS Nano 2024. [PMID: 38315563 PMCID: PMC10883052 DOI: 10.1021/acsnano.3c09602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2024]
Abstract
The family of two-dimensional (2D) van der Waals (vdW) materials provides a playground for tuning structural and magnetic interactions to create a wide variety of spin textures. Of particular interest is the ferromagnetic compound Fe5GeTe2 that we show displays a range of complex spin textures as well as complex crystal structures. Here, using a high-brailliance laboratory X-ray source, we show that the majority (1 × 1) Fe5GeTe2 (FGT5) phase exhibits a structure that was previously considered as being centrosymmetric but rather lacks inversion symmetry. In addition, FGT5 exhibits a minority phase that exhibits a long-range ordered (√3 × √3)-R30° superstructure. This superstructure is highly interesting in that it is innately 2D without any lattice periodicity perpendicular to the vdW layers, and furthermore, the superstructure is a result of ordered Te vacancies in one of the topmost layers of the FGT5 sheets rather than being a result of vertical Fe ordering as earlier suggested. We show, from direct real-space magnetic imaging, evidence for three distinct magnetic ground states in lamellae of FGT5 that are stabilized with increasing lamella thickness, namely, a multidomain state, a stripe phase, and an unusual fractal state. In the stripe phase we also observe unconventional type-I and type-II bubbles where the spin texture in the central region of the bubbles is nonuniform, unlike conventional bubbles. In addition, we find a bobber or a cocoon-like spin texture in thick (∼170 μm) FGT5 that emerges from the fractal state in the presence of a magnetic field. Among all the 2D vdW magnets we have thus demonstrated that FGT5 hosts perhaps the richest variety of magnetic phases that, thereby, make it a highly interesting platform for the subtle tuning of magnetic interactions.
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Affiliation(s)
- Ajesh K Gopi
- 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
| | - Ankit K Sharma
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale) D-06120, Germany
| | - Anirban Chakraborty
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale) D-06120, Germany
| | - Souvik Das
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale) D-06120, Germany
| | - Hakan Deniz
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale) D-06120, Germany
| | - Arthur Ernst
- Johannes Kepler University, Altenbergerstraβe 69, Linz 4040, Austria
| | - Binoy K Hazra
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale) D-06120, Germany
| | - Holger L Meyerheim
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale) D-06120, Germany
| | - Stuart S P Parkin
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale) D-06120, Germany
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5
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Williams J, Faley MI, Vas JV, Lu PH, Dunin-Borkowski RE. TEM sample preparation of lithographically patterned permalloy nanostructures on silicon nitride membranes. Beilstein J Nanotechnol 2024; 15:1-12. [PMID: 38213573 PMCID: PMC10777327 DOI: 10.3762/bjnano.15.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Accepted: 11/28/2023] [Indexed: 01/13/2024]
Abstract
We have prepared ferromagnetic nanostructures intended for the investigation of high-frequency magnetization dynamics in permalloy (Py) nanodisks using Lorentz transmission electron microscopy (LTEM) and electron holography. Py nanodisks were fabricated on thin silicon nitride (SiN) membranes using three different fabrication methods: lift-off, ion beam etching (IBE), and stencil lithography. They were further analyzed using different instruments, including scanning electron microscopy, LTEM, and electron holography. A bilayer of positive PMMA resist was utilized in the first fabrication method to form an undercut structure that guarantees a clean lift-off procedure. The second approach used dry etching with an Ar beam to etch a thin Py film, while an electron-beam-patterned negative resist mask kept the desired structure. In the third process, nanostencils (shadow masks) with submicrometer apertures were milled on SiN membranes using a focused ion beam. Furthermore, we have developed a new TEM sample preparation method, where we fabricated Py nanostructures on a bulk substrate with a SiN buffer layer and etched the substrate to create a thin SiN membrane under the Py nanostructure. Finally, we observed the vortex dynamics of the Py nanodisk under magnetic fields using LTEM and off-axis electron holography. A correlation between preparation methods and the properties of the Py nanostructures was made.
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Affiliation(s)
- Joshua Williams
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, 52425 Jülich, Germany
- Faculty of Engineering, University Duisburg-Essen, 47057 Duisburg, Germany
| | - Michael I Faley
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Joseph Vimal Vas
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Peng-Han Lu
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Rafal E Dunin-Borkowski
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, 52425 Jülich, Germany
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6
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Yu X, Liu Y, Iakoubovskii KV, Nakajima K, Kanazawa N, Nagaosa N, Tokura Y. Realization and Current-Driven Dynamics of Fractional Hopfions and Their Ensembles in a Helimagnet FeGe. Adv Mater 2023; 35:e2210646. [PMID: 36871172 DOI: 10.1002/adma.202210646] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Revised: 02/19/2023] [Indexed: 05/19/2023]
Abstract
3D topological spin textures-hopfions-are predicted in helimagnetic systems but are not experimentally confirmed thus far. By utilizing an external magnetic field and electric current in the present study, 3D topological spin textures are realized, including fractional hopfions with nonzero topological index, in a skyrmion-hosting helimagnet FeGe. Microsecond current pulses are employed to control the dynamics of the expansion and contraction of a bundle composed of a skyrmion and a fractional hopfion, as well as its current-driven Hall motion. This research approach has demonstrated the novel electromagnetic properties of fractional hopfions and their ensembles in helimagnetic systems.
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Affiliation(s)
- Xiuzhen Yu
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
| | - Yizhou Liu
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
| | | | - Kiyomi Nakajima
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
| | - Naoya Kanazawa
- Department of Applied Physics, University of Tokyo, Tokyo, 113-8656, Japan
| | - Naoto Nagaosa
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
- Department of Applied Physics, University of Tokyo, Tokyo, 113-8656, Japan
| | - Yoshinori Tokura
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
- Department of Applied Physics, University of Tokyo, Tokyo, 113-8656, Japan
- Tokyo College, University of Tokyo, Tokyo, 113-8656, Japan
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7
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Schöpf J, Thampi A, Milde P, Ivaneyko D, Kondovych S, Kononenko DY, Eng LM, Jin L, Yang L, Wysocki L, van Loosdrecht PHM, Richter K, Yershov KV, Wolf D, Lubk A, Lindfors-Vrejoiu I. Néel Skyrmion Bubbles in La 0.7Sr 0.3Mn 1-xRu xO 3 Multilayers. Nano Lett 2023; 23:3532-3539. [PMID: 37018631 DOI: 10.1021/acs.nanolett.3c00693] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Ferromagnetic La0.7Sr0.3Mn1-xRuxO3 epitaxial multilayers with controlled variation of the Ru/Mn content were synthesized to engineer canted magnetic anisotropy and variable exchange interactions, and to explore the possibility of generating a Dzyaloshinskii-Moriya interaction. The ultimate aim of the multilayer design is to provide the conditions for the formation of domains with nontrivial magnetic topology in an oxide thin film system. Employing magnetic force microscopy and Lorentz transmission electron microscopy in varying perpendicular magnetic fields, magnetic stripe domains separated by Néel-type domain walls as well as Néel skyrmions smaller than 100 nm in diameter were observed. These findings are consistent with micromagnetic modeling, taking into account a sizable Dzyaloshinskii-Moriya interaction arising from the inversion symmetry breaking and possibly from strain effects in the multilayer system.
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Affiliation(s)
- Jörg Schöpf
- II. Physics Institute, University of Cologne, 50937 Cologne, Germany
| | - Arsha Thampi
- Institute for Solid State Research, IFW Dresden, 01069 Dresden, Germany
| | - Peter Milde
- Institute of Applied Physics, TU Dresden, 01062 Dresden, Germany
| | - Dmytro Ivaneyko
- Institute of Applied Physics, TU Dresden, 01062 Dresden, Germany
| | - Svitlana Kondovych
- Institute for Theoretical Solid State Physics, IFW Dresden, 01069 Dresden, Germany
| | - Denys Y Kononenko
- Institute for Theoretical Solid State Physics, IFW Dresden, 01069 Dresden, Germany
| | - Lukas M Eng
- Institute of Applied Physics, TU Dresden, 01062 Dresden, Germany
- ct.qmat, Dresden-Würzburg Cluster of Excellence-EXC 2147, TU Dresden, 01062 Dresden, Germany
| | - Lei Jin
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
| | - Lin Yang
- II. Physics Institute, University of Cologne, 50937 Cologne, Germany
| | - Lena Wysocki
- II. Physics Institute, University of Cologne, 50937 Cologne, Germany
| | | | - Kornel Richter
- Faculty of Sciences, Pavol Jozef Safarik University, Park Angelinum 9, 041 54 Kosice, Slovakia
| | - Kostiantyn V Yershov
- Institute for Theoretical Solid State Physics, IFW Dresden, 01069 Dresden, Germany
- Bogolyubov Institute for Theoretical Physics of the National Academy of Sciences of Ukraine, 03143 Kyiv, Ukraine
| | - Daniel Wolf
- Institute for Solid State Research, IFW Dresden, 01069 Dresden, Germany
| | - Axel Lubk
- Institute for Solid State Research, IFW Dresden, 01069 Dresden, Germany
- Institute of Solid State and Materials Physics, TU Dresden, 01062 Dresden, Germany
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8
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McCray ARC, Li Y, Basnet R, Pandey K, Hu J, Phelan DP, Ma X, Petford-Long AK, Phatak C. Thermal Hysteresis and Ordering Behavior of Magnetic Skyrmion Lattices. Nano Lett 2022; 22:7804-7810. [PMID: 36129969 DOI: 10.1021/acs.nanolett.2c02275] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The physics of phase transitions in two-dimensional (2D) systems underpins research in diverse fields including statistical mechanics, nanomagnetism, and soft condensed matter. However, many aspects of 2D phase transitions are still not well understood, including the effects of interparticle potential, polydispersity, and particle shape. Magnetic skyrmions are chiral spin-structure quasi-particles that form two-dimensional lattices. Here, we show, by real-space imaging using in situ cryo-Lorentz transmission electron microscopy coupled with machine learning image analysis, the ordering behavior of Néel skyrmion lattices in van der Waals Fe3GeTe2. We demonstrate a distinct change in the skyrmion size distribution during field-cooling, which leads to a loss of lattice order and an evolution of the skyrmion liquid phase. Remarkably, the lattice order is restored during field heating and demonstrates a thermal hysteresis. This behavior is explained by the skyrmion energy landscape and demonstrates the potential to control the lattice order in 2D phase transitions.
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Affiliation(s)
- Arthur R C McCray
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
- Applied Physics Program, Northwestern University, Evanston, Illinois 60208, United States
| | - Yue Li
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Rabindra Basnet
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, United States
| | - Krishna Pandey
- Materials Science and Engineering Program, University of Arkansas, Fayetteville, Arkansas 72701, United States
| | - Jin Hu
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, United States
- Materials Science and Engineering Program, University of Arkansas, Fayetteville, Arkansas 72701, United States
| | - Daniel P Phelan
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Xuedan Ma
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Amanda K Petford-Long
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
| | - Charudatta Phatak
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
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9
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Chakraborty A, Srivastava AK, Sharma AK, Gopi AK, Mohseni K, Ernst A, Deniz H, Hazra BK, Das S, Sessi P, Kostanovskiy I, Ma T, Meyerheim HL, Parkin SSP. Magnetic Skyrmions in a Thickness Tunable 2D Ferromagnet from a Defect Driven Dzyaloshinskii-Moriya Interaction. Adv Mater 2022; 34:e2108637. [PMID: 35048455 DOI: 10.1002/adma.202108637] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Revised: 12/15/2021] [Indexed: 06/14/2023]
Abstract
There is considerable interest in van der Waals (vdW) materials as potential hosts for chiral skyrmionic spin textures. Of particular interest is the ferromagnetic, metallic compound Fe3 GeTe2 (FGT), which has a comparatively high Curie temperature (150-220 K). Several recent studies have reported the observation of chiral Néel skyrmions in this compound, which is inconsistent with its presumed centrosymmetric structure. Here the observation of Néel type skyrmions in single crystals of FGT via Lorentz transmission electron microscopy (LTEM) is reported. It is shown from detailed X-ray diffraction structure analysis that FGT lacks an inversion symmetry as a result of an asymmetric distribution of Fe vacancies. This vacancy-induced breaking of the inversion symmetry of this compound is a surprising and novel observation and is a prerequisite for a Dzyaloshinskii-Moriya vector exchange interaction which accounts for the chiral Néel skyrmion phase. This phenomenon is likely to be common to many 2D vdW materials and suggests a path to the preparation of many such acentric compounds. Furthermore, it is found that the skyrmion size in FGT is strongly dependent on its thickness: the skyrmion size increases from ≈100 to ≈750 nm as the thickness of the lamella is increased from ≈90 nm to ≈2 µm. This extreme size tunability is a feature common to many low symmetry ferro- and ferri-magnetic compounds.
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Affiliation(s)
- Anirban Chakraborty
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Abhay K Srivastava
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Ankit K Sharma
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Ajesh K Gopi
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Katayoon Mohseni
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Arthur Ernst
- Johannes Kepler University, Altenbergerstrβe 69, Linz, 4040, Austria
| | - Hakan Deniz
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Binoy Krishna Hazra
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Souvik Das
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Paolo Sessi
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Ilya Kostanovskiy
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Tianping Ma
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Holger L Meyerheim
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
| | - Stuart S P Parkin
- Department for Nano-Systems from Ions, Spins, and Electrons (NISE), Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120, Halle(Saale), Germany
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10
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Karube K, Peng L, Masell J, Hemmida M, Krug von Nidda HA, Kézsmárki I, Yu X, Tokura Y, Taguchi Y. Doping Control of Magnetic Anisotropy for Stable Antiskyrmion Formation in Schreibersite (Fe,Ni) 3 P with S 4 symmetry. Adv Mater 2022; 34:e2108770. [PMID: 35032408 DOI: 10.1002/adma.202108770] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 01/06/2022] [Indexed: 06/14/2023]
Abstract
Magnetic skyrmions, vortex-like topological spin textures, have attracted much interest in a wide range of research fields from fundamental physics to spintronics applications. Recently, growing attention is also paid to antiskyrmions emerging with opposite topological charge in non-centrosymmetric magnets with D2d or S4 symmetry. In these magnets, complex interplay among anisotropic Dzyaloshinskii-Moriya interaction, uniaxial magnetic anisotropy, and magnetic dipolar interactions generates various magnetic textures. However, the precise role of these magnetic interactions in stabilizing antiskyrmions remains to be elucidated. In this work, the uniaxial magnetic anisotropy of schreibersite (Fe,Ni)3 P with S4 symmetry is controlled by doping and its impact on the stability of antiskyrmions is investigated. The authors' magnetometry study, supported by ferromagnetic resonance spectroscopy, shows that the variation of the Ni content and slight doping with 4d transition metals considerably change the magnetic anisotropy. In particular, doping with Pd induces easy-axis anisotropy, giving rise to formation of antiskyrmions, while a temperature-induced spin reorientation is observed in an Rh-doped compound. In combination with Lorentz transmission electron microscopy and micromagnetic simulations, the stability of antiskyrmion as functions of uniaxial anisotropy and demagnetization energy is quantitatively analyzed, and demonstrated that subtle balance between them is necessary to stabilize the antiskyrmions.
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Affiliation(s)
- Kosuke Karube
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
| | - Licong Peng
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
| | - Jan Masell
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
- Institute of Theoretical Solid State Physics, Karlsruhe Institute of Technology (KIT), Karlsruhe, 76049, Germany
| | - Mamoun Hemmida
- Experimental Physics V, University of Augsburg, Augsburg, 86135, Germany
| | | | - István Kézsmárki
- Experimental Physics V, University of Augsburg, Augsburg, 86135, Germany
| | - Xiuzhen Yu
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
| | - Yoshinori Tokura
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, 113-8656, Japan
- Tokyo College, University of Tokyo, Bunkyo-ku, 113-8656, Japan
| | - Yasujiro Taguchi
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan
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11
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Schönenberger T, Huang P, Brun LD, Guanghao L, Magrez A, Carbone F, Rønnow HM. Direct Visualisation of Skyrmion Lattice Defect Alignment at Grain Boundaries. Nanoscale Res Lett 2022; 17:20. [PMID: 35089439 PMCID: PMC8799828 DOI: 10.1186/s11671-022-03654-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Accepted: 01/05/2022] [Indexed: 06/14/2023]
Abstract
We present a method to directly visualise a statistical analysis of skyrmion defect alignment at grain boundaries in the skyrmion host [Formula: see text]OSeO3. Using Lorentz transmission electron microscopy, we collected large data sets with several hundreds of frames containing skyrmion lattices with grain boundaries in them. To address the behaviour of strings of dislocations in these grain boundaries, we developed an algorithm to automatically extract and classify strings of dislocations separating the grains. This way we circumvent the problem of having to create configurations with well-defined relative grain orientations by performing a statistical analysis on a dynamically rearranging image sequence. With this statistical method, we are able to experimentally extract the relationship between grain boundary alignment and defect spacing and find an agreement with geometric expectations. The algorithms used can be extended to other types of lattices such as Abrikosov lattices or colloidal systems in optical microscopy.
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Affiliation(s)
- Thomas Schönenberger
- Laboratory for Quantum Magnetism (LQM), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Ping Huang
- State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an, China
| | - Lawrence D. Brun
- Laboratory for Quantum Magnetism (LQM), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Li Guanghao
- Laboratory for Quantum Magnetism (LQM), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Arnaud Magrez
- Laboratory for Quantum Magnetism (LQM), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Fabrizio Carbone
- Laboratory for Quantum Magnetism (LQM), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Henrik M. Rønnow
- Laboratory for Quantum Magnetism (LQM), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
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12
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Denneulin T, Caron J, Hoffmann M, Lin M, Tan HK, Kovács A, Blügel S, Dunin-Borkowski RE. Off-axis electron holography of Néel-type skyrmions in multilayers of heavy metals and ferromagnets. Ultramicroscopy 2021; 220:113155. [PMID: 33181365 DOI: 10.1016/j.ultramic.2020.113155] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2020] [Revised: 09/28/2020] [Accepted: 10/22/2020] [Indexed: 11/22/2022]
Abstract
Magnetic skyrmions are complex swirling spin structures that are of interest for applications in energy-efficient memories and logic technologies. Multilayers of heavy metals and ferromagnets have been shown to host magnetic skyrmions at room temperature. Lorentz transmission electron microscopy is often used to study magnetic domain structures in multilayer samples using mainly Fresnel defocus imaging. Here, off-axis electron holography is used to obtain in-focus electron optical phase images of Néel-type domains and skyrmions in an Ir/Fe/Co/Pt multilayer sample. The preparation of the sample, reconstruction of the holograms and influence of sample tilt angle on the signal-to-noise ratio in the phase images are discussed. A good agreement is found between images of individual skyrmions that are stabilized using an external magnetic field and simulated images based on theoretical models of Néel-type skyrmions.
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13
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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. Adv Mater 2020; 32:e2002043. [PMID: 32484269 DOI: 10.1002/adma.202002043] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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.
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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
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14
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Ding B, Li Z, Xu G, Li H, Hou Z, Liu E, Xi X, Xu F, Yao Y, Wang W. Observation of Magnetic Skyrmion Bubbles in a van der Waals Ferromagnet Fe 3GeTe 2. Nano Lett 2020; 20:868-873. [PMID: 31869236 DOI: 10.1021/acs.nanolett.9b03453] [Citation(s) in RCA: 67] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Two-dimensional (2D) van der Waals (vdW) magnetic materials have recently been introduced as a new horizon in materials science, and they enable potential applications for next-generation spintronic devices. Here, in this communication, the observations of stable Bloch-type magnetic skyrmions in single crystals of 2D vdW Fe3GeTe2 (FGT) are reported by using in situ Lorentz transmission electron microscopy (TEM). We find the ground-state magnetic stripe domains in FGT transform into skyrmion bubbles when an external magnetic field is applied perpendicularly to the (001) thin plate with temperatures below the Curie temperature TC. Most interestingly, a hexagonal lattice of skyrmion bubbles is obtained via field-cooling manipulation with magnetic field applied along the [001] direction. Owing to their topological stability, the skyrmion bubble lattices are stable to large field-cooling tilted angles and further reproduced by utilizing the micromagnetic simulations. These observations directly demonstrate that the 2D vdW FGT possesses a rich variety of topological spin textures, being of great promise for future applications in the field of spintronics.
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Affiliation(s)
- Bei Ding
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Zefang Li
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Guizhou Xu
- School of Materials Science and Engineering , Nanjing University of Science and Technology , Nanjing 210094 , China
| | - Hang Li
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
- University of Chinese Academy of Sciences , Beijing 100049 , China
| | - Zhipeng Hou
- South China Academy of Advanced Optoelectronics , South China Normal University , Guangzhou 510006 , China
| | - Enke Liu
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
| | - Xuekui Xi
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
| | - Feng Xu
- School of Materials Science and Engineering , Nanjing University of Science and Technology , Nanjing 210094 , China
| | - Yuan Yao
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
| | - Wenhong Wang
- Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
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15
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Srivastava AK, Devi P, Sharma AK, Ma T, Deniz H, Meyerheim HL, Felser C, Parkin SSP. Observation of Robust Néel Skyrmions in Metallic PtMnGa. Adv Mater 2020; 32:e1904327. [PMID: 31880023 DOI: 10.1002/adma.201904327] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2019] [Revised: 11/03/2019] [Indexed: 06/10/2023]
Abstract
Over the past decade the family of chiral noncollinear spin textures has continued to expand with the observation in metallic compounds of Bloch-like skyrmions in several B20 compounds, and antiskyrmions in a tetragonal inverse Heusler. Néel like skyrmions in bulk crystals with broken inversion symmetry have recently been seen in two distinct nonmetallic compounds, GaV4 S8 and VOSe2 O5 at low temperatures (below ≈13 K) only. Here, the first observation of bulk Néel skyrmions in a metallic compound PtMnGa and, moreover, at high temperatures up to ≈220 K is reported. Lorentz transmission electron microscopy reveals the chiral Néel character of the skyrmions. A strong variation is reported of the size of the skyrmions on the thickness of the lamella in which they are confined, varying by a factor of 7 as the thickness is varied from ≈90 nm to ≈4 µm. Moreover, the skyrmions are highly robust to in-plane magnetic fields and can be stabilized in a zero magnetic field using suitable field-cooling protocols over a very broad temperature range to as low as 5 K. These properties, together with the possibility of manipulating skyrmions in metallic PtMnGa via current induced spin-orbit torques, make them extremely exciting for future spintronic applications.
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Affiliation(s)
- 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
| | - Parul Devi
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straβe 40, 01187, Dresden, 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
| | - 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
| | - Hakan Deniz
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale), D-06120, Germany
| | - Holger L Meyerheim
- Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale), D-06120, Germany
| | - Claudia Felser
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straβe 40, 01187, Dresden, 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
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16
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Loudon JC, Twitchett‐Harrison AC, Cortés‐Ortuño D, Birch MT, Turnbull LA, Štefančič A, Ogrin FY, Burgos‐Parra EO, Bukin N, Laurenson A, Popescu H, Beg M, Hovorka O, Fangohr H, Midgley PA, Balakrishnan G, Hatton PD. Do Images of Biskyrmions Show Type-II Bubbles? Adv Mater 2019; 31:e1806598. [PMID: 30844122 PMCID: PMC9285551 DOI: 10.1002/adma.201806598] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Revised: 01/31/2019] [Indexed: 06/09/2023]
Abstract
The intense research effort investigating magnetic skyrmions and their applications for spintronics has yielded reports of more exotic objects including the biskyrmion, which consists of a bound pair of counter-rotating vortices of magnetization. Biskyrmions have been identified only from transmission electron microscopy images and have not been observed by other techniques, nor seen in simulations carried out under realistic conditions. Here, quantitative Lorentz transmission electron microscopy, X-ray holography, and micromagnetic simulations are combined to search for biskyrmions in MnNiGa, a material in which they have been reported. Only type-I and type-II magnetic bubbles are found and images purported to show biskyrmions can be explained as type-II bubbles viewed at an angle to their axes. It is not the magnetization but the magnetic flux density resulting from this object that forms the counter-rotating vortices.
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Affiliation(s)
- James C. Loudon
- Department of Materials Science and MetallurgyUniversity of Cambridge27 Charles Babbage RoadCambridgeCB3 0FSUK
| | | | - David Cortés‐Ortuño
- Faculty of Engineering and Physical SciencesUniversity of SouthamptonSouthamptonSO17 1BJUK
| | - Max T. Birch
- Department of PhysicsUniversity of DurhamDurhamDH1 3LEUK
| | | | - Aleš Štefančič
- Department of PhysicsUniversity of WarwickCoventryCV4 7ALUK
| | - Feodor Y. Ogrin
- School of Physics and AstronomyUniversity of ExeterExeterEX4 4QLUK
| | | | - Nicholas Bukin
- School of Physics and AstronomyUniversity of ExeterExeterEX4 4QLUK
| | - Angus Laurenson
- School of Physics and AstronomyUniversity of ExeterExeterEX4 4QLUK
| | - Horia Popescu
- Synchrotron SOLEILSaint Aubin, BP 4891192Gif‐sur‐YvetteFrance
| | - Marijan Beg
- Faculty of Engineering and Physical SciencesUniversity of SouthamptonSouthamptonSO17 1BJUK
- European XFEL GmbHHolzkoppel 422869SchenefeldGermany
| | - Ondrej Hovorka
- Faculty of Engineering and Physical SciencesUniversity of SouthamptonSouthamptonSO17 1BJUK
| | - Hans Fangohr
- Faculty of Engineering and Physical SciencesUniversity of SouthamptonSouthamptonSO17 1BJUK
- European XFEL GmbHHolzkoppel 422869SchenefeldGermany
| | - Paul A. Midgley
- Department of Materials Science and MetallurgyUniversity of Cambridge27 Charles Babbage RoadCambridgeCB3 0FSUK
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17
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Li Y, Paterson GW, Macauley GM, Nascimento FS, Ferguson C, Morley SA, Rosamond MC, Linfield EH, MacLaren DA, Macêdo R, Marrows CH, McVitie S, Stamps RL. Superferromagnetism and Domain-Wall Topologies in Artificial "Pinwheel" Spin Ice. ACS Nano 2019; 13:2213-2222. [PMID: 30588800 DOI: 10.1021/acsnano.8b08884] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
For over ten years, arrays of interacting single-domain nanomagnets, referred to as artificial spin ices, have been engineered with the aim to study frustration in model spin systems. Here, we use Fresnel imaging to study the reversal process in "pinwheel" artificial spin ice, a modified square ASI structure obtained by rotating each island by some angle about its midpoint. Our results demonstrate that a simple 45° rotation changes the magnetic ordering from antiferromagnetic to ferromagnetic, creating a superferromagnet which exhibits mesoscopic domain growth mediated by domain wall nucleation and coherent domain propagation. We observe several domain-wall configurations, most of which are direct analogues to those seen in continuous ferromagnetic films. However, charged walls also appear due to the geometric constraints of the system. Changing the orientation of the external magnetic field allows control of the nature of the spin reversal with the emergence of either one- or two-dimensional avalanches. This property of pinwheel ASI could be employed to tune devices based on magnetotransport phenomena such as Hall circuits.
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Affiliation(s)
- Yue Li
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Gary W Paterson
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Gavin M Macauley
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Fabio S Nascimento
- Departamento de Física , Universidade Federal de Viçosa , Viçosa 36570-900 , Minas Gerais , Brazil
| | - Ciaran Ferguson
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Sophie A Morley
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , United Kingdom
- Department of Physics , University of California , Santa Cruz , California 95064 , United States
| | - Mark C Rosamond
- School of Electronic and Electrical Engineering , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Edmund H Linfield
- School of Electronic and Electrical Engineering , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Donald A MacLaren
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Rair Macêdo
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Christopher H Marrows
- School of Physics and Astronomy , University of Leeds , Leeds LS2 9JT , United Kingdom
| | - Stephen McVitie
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Robert L Stamps
- SUPA, School of Physics and Astronomy , University of Glasgow , Glasgow G12 8QQ , United Kingdom
- Department of Physics and Astronomy , University of Manitoba , Manitoba R3T 2N2 , Canada
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18
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Hou Z, Zhang Q, Xu G, Zhang S, Gong C, Ding B, Li H, Xu F, Yao Y, Liu E, Wu G, Zhang XX, Wang W. Manipulating the Topology of Nanoscale Skyrmion Bubbles by Spatially Geometric Confinement. ACS Nano 2019; 13:922-929. [PMID: 30605309 DOI: 10.1021/acsnano.8b09689] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The discovery of magnetic skyrmion bubbles in centrosymmetric magnets has been receiving increasing interest from the research community, due to the fascinating physics of topological spin textures and its possible applications to spintronics. However, key challenges remain, such as how to manipulate the nucleation of skyrmion bubbles to exclude the trivial bubbles or metastable skyrmion bubbles that usually coexist with skyrmion bubbles in the centrosymmetric magnets. Here, we report having performed this task by applying spatially geometric confinement to a centrosymmetric frustrated Fe3Sn2 magnet. We demonstrate that the spatially geometric confinement can indeed stabilize the skyrmion bubbles by effectively suppressing the formation of trivial bubbles and metastable skyrmion bubbles. We also show that the critical magnetic field for the nucleation of the skyrmion bubbles in the confined Fe3Sn2 nanostripes is drastically less, by an order of magnitude, than that required in the thin plate without geometrical confinement. By analyzing how the width and thickness of the nanostripes affect the spin textures of skyrmion bubbles, we infer that the topological transition of skyrmion bubbles is closely related to the dipole-dipole interaction, which we find is consistent with theoretical simulations. The results presented here bring us closer to achieving the fabrication of skyrmion-based racetrack memory devices.
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Affiliation(s)
- Zhipeng Hou
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
- Physical Science and Engineering , King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900 , Saudi Arabia
| | - Qiang Zhang
- Physical Science and Engineering , King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900 , Saudi Arabia
| | - Guizhou Xu
- School of Materials Science and Engineering , Nanjing University of Science and Technology , Nanjing 210094 , China
| | - Senfu Zhang
- Physical Science and Engineering , King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900 , Saudi Arabia
| | - Chen Gong
- Physical Science and Engineering , King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900 , Saudi Arabia
| | - Bei Ding
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
| | - Hang Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
| | - Feng Xu
- School of Materials Science and Engineering , Nanjing University of Science and Technology , Nanjing 210094 , China
| | - Yuan Yao
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
| | - Enke Liu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
| | - Guangheng Wu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
| | - Xi-Xiang Zhang
- Physical Science and Engineering , King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900 , Saudi Arabia
| | - Wenhong Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , China
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19
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Abstract
Topological concepts play an important role in, and provide unique insights into, many physical phenomena. In particular topological defects have become an active area of research due to their relevance to diverse systems including condensed matter and the early universe. These defects arise in systems during phase transitions or symmetry-breaking operations that lead to a specific configuration of the order parameter that is stable against external perturbations. In this work, we experimentally show that excitations or defects carrying magnetic charge in artificial spin ices introduce a topological defect in incident coherent electron waves. This results in the formation of a localized electron vortex beam carrying orbital angular momentum that is directly correlated with the magnetic charge. This work provides unique insight into the interaction of electrons with magnetically charged excitations and the effect on their topology thereby opening new possibilities to explore exotic scattering and quantum effects in nanoscale condensed-matter systems.
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Affiliation(s)
- Charudatta Phatak
- Materials Science Division , Argonne National Laboratory , Lemont , Illinois 60439 , United States
| | - Amanda Petford-Long
- Materials Science Division , Argonne National Laboratory , Lemont , Illinois 60439 , United States
- Department of Materials Science and Engineering , Northwestern University , Evanston , Illinois 60208 , United States
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20
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Huang P, Cantoni M, Kruchkov A, Rajeswari J, Magrez A, Carbone F, Rønnow HM. In Situ Electric Field Skyrmion Creation in Magnetoelectric Cu 2OSeO 3. Nano Lett 2018; 18:5167-5171. [PMID: 30040904 DOI: 10.1021/acs.nanolett.8b02097] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Exploiting additional degrees of freedom in solid-state materials may be the most-promising solution when approaching the quantum limit of Moore's law for the conventional electronic industry. Recently discovered topologically nontrivial spin textures, skyrmions, are outstanding among such possibilities. However, the controlled creation of skyrmions, especially by electric means, remains a pivotal challenge in technological applications. Here, we report that skyrmions can be created locally via electric field in the magnetoelectric helimagnet Cu2OSeO3. Using Lorentz transmission electron microscopy, we successfully write skyrmions in situ from a helical-spin background. Our discovery is highly coveted because it implies that skyrmionics can be integrated into modern field effect transistor based electronic technology, in which very low energy dissipation can be achieved and, hence, realize a large step forward toward its practical applications.
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Affiliation(s)
| | - Marco Cantoni
- Centre Interdisciplinaire de Microscopie Électronique (CIME) , École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne , Switzerland
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21
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Kashyap I, Jin YM, Vetter EP, Floro JA, De Graef M. Lorentz Transmission Electron Microscopy Image Simulations of Experimental Nano-Chessboard Observations in Co-Pt Alloys. Microsc Microanal 2018; 24:221-226. [PMID: 29855395 DOI: 10.1017/s143192761800034x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The magnetization configuration of a novel nano-chessboard structure consisting of L10 and L12 phases in a Co40Pt60 alloy is investigated using Lorentz transmission electron microscopy (LTEM) and micro-magnetic simulations. We show high-resolution LTEM images of nano-size magnetic features acquired through spherical aberration correction in Lorentz Fresnel mode. Phase reconstructions and LTEM image simulations are carried out to fully understand the magnetic microstructure. The experimental Fresnel images of the nano-chessboard structure show zig-zag shaped magnetic domain walls at the inter-phase boundaries between L10 and L12 phases. A circular magnetization distribution with vortex and anti-vortex type arrangement is evident in the phase reconstructed magnetic induction maps as well as simulated maps. The magnetic contrast in experimental LTEM images is interpreted with the help of magnetic induction maps simulated for various relative electron beam-sample orientations inside the TEM.
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Affiliation(s)
- Isha Kashyap
- 1Department of Materials Science and Engineering,Carnegie Mellon University,5000 Forbes Avenue,Pittsburgh,PA 15213,USA
| | - Yongmei M Jin
- 2Department of Materials Science and Engineering,Michigan Technological University,Houghton,MI 49931,USA
| | - Eric P Vetter
- 3Department of Materials Science and Engineering,University of Virginia,Charlottesville,VA 22903,USA
| | - Jerrold A Floro
- 3Department of Materials Science and Engineering,University of Virginia,Charlottesville,VA 22903,USA
| | - Marc De Graef
- 1Department of Materials Science and Engineering,Carnegie Mellon University,5000 Forbes Avenue,Pittsburgh,PA 15213,USA
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22
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Hou Z, Zhang Q, Xu G, Gong C, Ding B, Wang Y, Li H, Liu E, Xu F, Zhang H, Yao Y, Wu G, Zhang XX, Wang W. Creation of Single Chain of Nanoscale Skyrmion Bubbles with Record-High Temperature Stability in a Geometrically Confined Nanostripe. Nano Lett 2018; 18:1274-1279. [PMID: 29299928 DOI: 10.1021/acs.nanolett.7b04900] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Nanoscale topologically nontrivial spin textures, such as magnetic skyrmions, have been identified as promising candidates for the transport and storage of information for spintronic applications, notably magnetic racetrack memory devices. The design and realization of a single skyrmion chain at room temperature (RT) and above in the low-dimensional nanostructures are of great importance for future practical applications. Here, we report the creation of a single skyrmion bubble chain in a geometrically confined Fe3Sn2 nanostripe with a width comparable to the featured size of a skyrmion bubble. Systematic investigations on the thermal stability have revealed that the single chain of skyrmion bubbles can keep stable at temperatures varying from RT up to a record-high temperature of 630 K. This extreme stability can be ascribed to the weak temperature-dependent magnetic anisotropy and the formation of edge states at the boundaries of the nanostripes. The realization of the highly stable skyrmion bubble chain in a geometrically confined nanostructure is a very important step toward the application of skyrmion-based spintronic devices.
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Affiliation(s)
- Zhipeng Hou
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
- Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Saudi Arabia
| | - Qiang Zhang
- Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Saudi Arabia
| | - Guizhou Xu
- School of Materials Science and Engineering, Nanjing University of Science and Technology , Nanjing 210094, China
| | - Chen Gong
- Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Saudi Arabia
| | - Bei Ding
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Yue Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Hang Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Enke Liu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Feng Xu
- School of Materials Science and Engineering, Nanjing University of Science and Technology , Nanjing 210094, China
| | - Hongwei Zhang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Yuan Yao
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Guangheng Wu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Xi-Xiang Zhang
- Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Saudi Arabia
| | - Wenhong Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
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23
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Shibata K, Tanigaki T, Akashi T, Shinada H, Harada K, Niitsu K, Shindo D, Kanazawa N, Tokura Y, Arima TH. Current-Driven Motion of Domain Boundaries between Skyrmion Lattice and Helical Magnetic Structure. Nano Lett 2018; 18:929-933. [PMID: 29345472 DOI: 10.1021/acs.nanolett.7b04312] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
To utilize magnetic skyrmions, nanoscale vortex-like magnetic structures, experimental elucidation of their dynamics against current application in various circumstances such as in confined structure and mixture of different magnetic phases is indispensable. Here, we investigate the current-induced dynamics of the coexistence state of magnetic skyrmions and helical magnetic structure in a thin plate of B20-type helimagnet FeGe in terms of in situ real-space observation using Lorentz transmission electron microscopy. Current pulses with various heights and widths were applied, and the change of the magnetic domain distribution was analyzed using a machine-learning technique. The observed average driving direction of the two-magnetic-state domain boundary is opposite to the applied electric current, indicating ferromagnetic s-d exchange coupling in the spin-transfer torque mechanism. The evaluated driving distance tends to increase with increasing the pulse duration time, current density (>1 × 109 A/m2), and sample temperature, providing valuable information about hitherto unknown current-induced dynamics of the skyrmion-lattice ensemble.
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Affiliation(s)
- Kiyou Shibata
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
| | - Toshiaki Tanigaki
- Research and Development Group, Hitachi Ltd., Hatoyama 350-0395, Japan
| | - Tetsuya Akashi
- Research and Development Group, Hitachi Ltd., Hatoyama 350-0395, Japan
| | - Hiroyuki Shinada
- Research and Development Group, Hitachi Ltd., Hatoyama 350-0395, Japan
| | - Ken Harada
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
| | - Kodai Niitsu
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
| | - Daisuke Shindo
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , Sendai 980-8577, Japan
| | - Naoya Kanazawa
- Department of Applied Physics, the University of Tokyo , Tokyo 113-8656, Japan
| | - Yoshinori Tokura
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
- Department of Applied Physics, the University of Tokyo , Tokyo 113-8656, Japan
| | - Taka-Hisa Arima
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
- Department of Advanced Materials Science, the University of Tokyo , Kashiwa 277-8561, Japan
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24
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Morikawa D, Yu X, Karube K, Tokunaga Y, Taguchi Y, Arima TH, Tokura Y. Deformation of Topologically-Protected Supercooled Skyrmions in a Thin Plate of Chiral Magnet Co 8Zn 8Mn 4. Nano Lett 2017; 17:1637-1641. [PMID: 28135106 DOI: 10.1021/acs.nanolett.6b04821] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Magnetic skyrmions in Co8Zn8Mn4 thin plates are observed to deform in a metastable state prepared in a magnetic-field-cooling process by way of the thermal-equilibrium skyrmion phase. In cooling, the disk-shape skyrmions change to bar- or L-shaped elongated form, whereas the skyrmion density is nearly conserved. The deformation of the skyrmions in the supercooled metastable phase is observed irrespective of the crystallographic orientation of the thin plate, whereas the elongation direction nearly aligns along the magnetic easy axis. It is proposed that the deformation should be induced by a large increase in magnetic modulation wavenumber when decreasing the temperature, whereas the topological protection of the skyrmions keeps the averaged skyrmion density constant.
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Affiliation(s)
- Daisuke Morikawa
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
| | - Xiuzhen Yu
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
| | - Kosuke Karube
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
| | - Yusuke Tokunaga
- Department of Advanced Materials Science, University of Tokyo , Kashiwa 277-8561, Japan
| | - Yasujiro Taguchi
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
| | - Taka-Hisa Arima
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
- Department of Advanced Materials Science, University of Tokyo , Kashiwa 277-8561, Japan
| | - Yoshinori Tokura
- RIKEN Center for Emergent Matter Science (CEMS) , Wako 351-0198, Japan
- Department of Applied Physics and Quantum Phase Electronics Center (QPEC), University of Tokyo , Tokyo 113-8656, Japan
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25
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Abstract
Magnetic skyrmions belong to a set of topologically nontrivial spin textures at the nanoscale that have received increased attention due to their emergent behavior and novel potential spintronic applications. Discovering materials systems that can host skyrmions at room temperature in the absence of external magnetic field is of crucial importance not only from a fundamental aspect, but also from a technological point of view. So far, the observations of skyrmions in bulk metallic ferromagnets have been limited to low temperatures and to materials that exhibit strong chiral interactions. Here we show the formation of nanoscale skyrmions in a nonchiral multiferroic material, which is ferromagnetic and ferroelastic, Ni2MnGa at room temperature without the presence of external magnetic fields. By using Lorentz transmission electron microscopy in combination with micromagnetic simulations, we elucidate their formation, behavior, and stability under applied magnetic fields at room temperature. The formation of skyrmions in a multiferroic material with no broken inversion symmetry presents new exciting opportunities for the exploration of the fundamental physics of topologically nontrivial spin textures.
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Affiliation(s)
- Charudatta Phatak
- Materials Science Division, Argonne National Laboratory , Lemont, Illinois 60439, United States
| | - Olle Heinonen
- Materials Science Division, Argonne National Laboratory , Lemont, Illinois 60439, United States
| | - Marc De Graef
- Department of Materials Science and Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Amanda Petford-Long
- Materials Science Division, Argonne National Laboratory , Lemont, Illinois 60439, United States
- Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States
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26
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Rajeswari J, Huang P, Mancini GF, Murooka Y, Latychevskaia T, McGrouther D, Cantoni M, Baldini E, White JS, Magrez A, Giamarchi T, Rønnow HM, Carbone F. Filming the formation and fluctuation of skyrmion domains by cryo- Lorentz transmission electron microscopy. Proc Natl Acad Sci U S A 2015; 112:14212-7. [PMID: 26578765 DOI: 10.1073/pnas.1513343112] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Magnetic skyrmions are promising candidates as information carriers in logic or storage devices thanks to their robustness, guaranteed by the topological protection, and their nanometric size. Currently, little is known about the influence of parameters such as disorder, defects, or external stimuli on the long-range spatial distribution and temporal evolution of the skyrmion lattice. Here, using a large (7.3 × 7.3 μm(2)) single-crystal nanoslice (150 nm thick) of Cu2OSeO3, we image up to 70,000 skyrmions by means of cryo-Lorentz transmission electron microscopy as a function of the applied magnetic field. The emergence of the skyrmion lattice from the helimagnetic phase is monitored, revealing the existence of a glassy skyrmion phase at the phase transition field, where patches of an octagonally distorted skyrmion lattice are also discovered. In the skyrmion phase, dislocations are shown to cause the emergence and switching between domains with different lattice orientations, and the temporal fluctuation of these domains is filmed. These results demonstrate the importance of direct-space and real-time imaging of skyrmion domains for addressing both their long-range topology and stability.
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27
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Kohn A, Habibi A, Mayo M. Experimental evaluation of the 'transport-of-intensity' equation for magnetic phase reconstruction in Lorentz transmission electron microscopy. Ultramicroscopy 2015; 160:44-56. [PMID: 26452194 DOI: 10.1016/j.ultramic.2015.09.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Revised: 09/20/2015] [Accepted: 09/26/2015] [Indexed: 11/29/2022]
Abstract
The 'transport-of-intensity' equation (TIE) is a general phase reconstruction methodology that can be applied to Lorentz transmission electron microscopy (TEM) through the use of Fresnel-contrast (defocused) images. We present an experimental study to test the application of the TIE for quantitative magnetic mapping in Lorentz TEM without aberration correction by examining sub-micrometer sized Ni80Fe20 (Permalloy) elements. For a JEOL JEM 2100F adapted for Lorentz microscopy, we find that quantitative magnetic phase reconstructions are possible for defoci distances ranging between approximately 200 μm and 800 μm. The lower limit originates from competing sources of image intensity variations in Fresnel-contrast images, namely structural defects and diffraction contrast. The upper defocus limit is due to a numerical error in the estimation of the intensity derivative based on three images. For magnetic domains, we show quantitative reconstructions of the product of the magnetic induction vector and thickness in element sizes down to approximately 100 nm in lateral size and 5 nm thick resulting in a minimal detection of 5Tnm. Three types of magnetic structures are tested in terms of phase reconstruction: vortex cores, domain walls, and element edges. We quantify vortex core structures at a diameter of 12 nm while the structures of domain walls and element edges are characterized qualitatively. Finally, we show by image simulations that the conclusions of this experimental study are relevant to other Lorentz TEM in which spherical aberration and defocus are dominant aberrations.
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Affiliation(s)
- Amit Kohn
- Department of Materials Science and Engineering, Faculty of Engineering, Tel Aviv University, 69978 Tel Aviv, Israel.
| | - Avihay Habibi
- Department of Materials Engineering, Ben-Gurion University of the Negev, 84105 Beer Sheva, Israel
| | - Martin Mayo
- Department of Materials Engineering, Ben-Gurion University of the Negev, 84105 Beer Sheva, Israel
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28
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Humphrey E, Phatak C, Petford-Long AK, De Graef M. Separation of electrostatic and magnetic phase shifts using a modified transport-of-intensity equation. Ultramicroscopy 2014; 139:5-12. [PMID: 24513573 DOI: 10.1016/j.ultramic.2014.01.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Revised: 01/02/2014] [Accepted: 01/17/2014] [Indexed: 12/01/2022]
Abstract
We introduce a new approach for the separation of the electrostatic and magnetic components of the electron wave phase shift, based on the transport-of-intensity equation (TIE) formalism. We derive two separate TIE-like equations, one for each of the phase shift components. We use experimental results on FeCoB and Permalloy patterned islands to illustrate how the magnetic and electrostatic longitudinal derivatives can be computed. The main advantage of this new approach is the fact that the differences in the power spectra of the two phase components (electrostatic phase shifts often have significant power in the higher frequencies) can be accommodated by the selection of two different Tikhonov regularization parameters for the two phase reconstructions. The extra computational demands of the method are more than compensated by the improved phase reconstruction results.
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Affiliation(s)
- E Humphrey
- Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - C Phatak
- Argonne National Laboratory, Argonne, IL 60439, USA
| | | | - M De Graef
- Carnegie Mellon University, Pittsburgh, PA 15213, USA
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