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Pankratova M, Eriksson O, Bergman A. Zero-field magnetic skyrmions in exchange-biased ferromagnetic-antiferromagnetic bilayers. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:385803. [PMID: 38848725 DOI: 10.1088/1361-648x/ad5598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2024] [Accepted: 06/07/2024] [Indexed: 06/09/2024]
Abstract
We report on the stabilization of ferromagnetic skyrmions in zero external magnetic fields, in exchange-biased systems composed of ferromagnetic-antiferromagnetic (FM-AFM) bilayers. By performing atomistic spin dynamics simulations, we study cases of compensated, uncompensated, and partly uncompensated FM-AFM interfaces, and investigate the impact of important parameters such as temperature, inter-plane exchange interaction, Dzyaloshinskii-Moriya interaction, and magnetic anisotropy on the skyrmions appearance and stability. The model with an uncompensated FM-AFM interface leads to the stabilization of individual skyrmions and skyrmion lattices in the FM layer, caused by the effective field from the AFM instead of an external magnetic field. Similarly, in the case of a fully compensated FM-AFM interface, we show that FM skyrmions can be stabilized. We also demonstrate that accounting for interface roughness leads to stabilization of skyrmions both in compensated and uncompensated interface. Moreover, in bilayers with a rough interface, skyrmions in the FM layer are observed for a wide range of exchange interaction values through the FM-AFM interface, and the chirality of the skyrmions depends critically on the exchange interaction.
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Affiliation(s)
- M Pankratova
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden
- Wallenberg Initiative Materials Science for Sustainability, Uppsala University, 75121 Uppsala, Sweden
| | - O Eriksson
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden
- Wallenberg Initiative Materials Science for Sustainability, Uppsala University, 75121 Uppsala, Sweden
| | - A Bergman
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden
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Cao Y, Ding H, Zuo Y, Li X, Zhao Y, Li T, Lei N, Cao J, Si M, Xi L, Jia C, Xue D, Yang D. Acoustic spin rotation in heavy-metal-ferromagnet bilayers. Nat Commun 2024; 15:1013. [PMID: 38307850 PMCID: PMC10837457 DOI: 10.1038/s41467-024-45317-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Accepted: 01/19/2024] [Indexed: 02/04/2024] Open
Abstract
Through pumping a spin current from ferromagnet into heavy metal (HM) via magnetization precession, parts of the injected spins are in-plane rotated by the lattice vibration, namely acoustic spin rotation (ASR), which manifests itself as an inverse spin Hall voltage in HM with an additional 90° difference in angular dependency. When reversing the stacking order of bilayer with a counter-propagating spin current or using HMs with an opposite spin Hall angle, such ASR voltage shows the same sign, strongly suggesting that ASR changes the rotation direction due to interface spin-orbit interaction. With the drift-diffusion model of spin transport, we quantify the efficiency of ASR up to 30%. The finding of ASR endows the acoustic device with an ability to manipulate spin, and further reveals a new spin-orbit coupling between spin current and lattice vibration.
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Affiliation(s)
- Yang Cao
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Hao Ding
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Yalu Zuo
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Xiling Li
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Yibing Zhao
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Tong Li
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Na Lei
- Fert Beijing Institute, MIIT Key Laboratory of Spintronics, School of Integrated Circuit Science and Engineering, Beihang University, Beijing, 100191, China
| | - Jiangwei Cao
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Mingsu Si
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Li Xi
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Chenglong Jia
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China
| | - Desheng Xue
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China.
| | - Dezheng Yang
- Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou, 730000, China.
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Challab N, Roussigné Y, Chérif SM, Gabor M, Belmeguenai M. Magnetic Damping and Dzyaloshinskii-Moriya Interactions in Pt/Co 2FeAl/MgO Systems Grown on Si and MgO Substrates. MATERIALS (BASEL, SWITZERLAND) 2023; 16:1388. [PMID: 36837017 PMCID: PMC9964789 DOI: 10.3390/ma16041388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Revised: 01/31/2023] [Accepted: 02/02/2023] [Indexed: 06/18/2023]
Abstract
Spin-pumping-induced damping and interfacial Dzyaloshinskii-Moriya interaction (iDMI) have been studied in Pt/Co2FeAl/MgO systems grown on Si or MgO substrates as a function of Pt and Co2FeAl (CFA) thicknesses. For this, we combined vibrating sample magnetometry (VSM), microstrip ferromagnetic resonance (MS-FMR), and Brillouin light scattering (BLS). VSM measurements of the magnetic moment at saturation per unit area revealed the absence of a magnetic dead layer in both systems, with a higher magnetization at saturation obtained for CFA grown on MgO. The key parameters governing the spin-dependent transport through the Pt/CFA interface, including the spin mixing conductance and the spin diffusion length, have been determined from the CFA and the Pt thickness dependence of the damping. BLS has been used to measure the spin wave non-reciprocity via the frequency mismatch between the Stokes and anti-Stokes lines. iDMI has been separated from the contribution of the interface perpendicular anisotropy difference between Pt/CFA and CFA/MgO. Our investigation revealed that both iDMI strength and spin pumping efficiency are higher for CFA-based systems grown on MgO due to its epitaxial growth confirmed by MS-FMR measurements of the in-plane magnetic anisotropy. This suggests that CFA grown on MgO could be a promising material candidate as a spin injection source via spin pumping and for other spintronic applications.
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Affiliation(s)
- Nabil Challab
- LSPM–CNRS, UPR 3407, Université Sorbonne Paris Nord, F-93430 Villetaneuse, France
| | - Yves Roussigné
- LSPM–CNRS, UPR 3407, Université Sorbonne Paris Nord, F-93430 Villetaneuse, France
| | - Salim Mourad Chérif
- LSPM–CNRS, UPR 3407, Université Sorbonne Paris Nord, F-93430 Villetaneuse, France
| | - Mihai Gabor
- Center for Superconductivity, Spintronics and Surface Science, Physics and Chemistry Department, Technical University of Cluj-Napoca, Str. Memorandumului No. 28, RO-400114 Cluj-Napoca, Romania
| | - Mohamed Belmeguenai
- LSPM–CNRS, UPR 3407, Université Sorbonne Paris Nord, F-93430 Villetaneuse, France
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Lepadatu S, Dobrynin A. Self-consistent computation of spin torques and magneto-resistance in tunnel junctions and magnetic read-heads with metallic pinhole defects. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:115801. [PMID: 36634368 DOI: 10.1088/1361-648x/acb2a6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Accepted: 01/12/2023] [Indexed: 06/17/2023]
Abstract
A three-dimensional self-consistent spin transport model is developed, which includes both tunnelling transport, leading to tunnelling magneto-resistance, as well as metallic transport, leading to giant magneto-resistance. An explicit solution to the drift-diffusion model is also derived, which allows analysing the effect of both the reference and free layer thickness on the spin-transfer torque polarization and field-like coefficient. It is shown the model developed here can be used to compute the signal-to-noise ratio in realistic magnetic read-heads, where spin torque-induced fluctuations and instabilities limit the maximum operating voltage. The effect of metallic pinhole defects in the insulator layer is also analysed. Increasing the area covered by pinholes results in a rapid degradation of the magneto-resistance, following an inverse dependence. Moreover, the spin torque angular dependence becomes skewed, similar to that obtained in fully metallic spin valves, and the spin-transfer torque polarization decreases. The same results are obtained when considering tunnel junctions with a single pinhole defect, but decreasing cross-sectional area, showing that even a single pinhole defect can significantly degrade the performance of tunnel junctions and magnetic read-heads below the 40 nm node.
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Affiliation(s)
- Serban Lepadatu
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston PR1 2HE, United Kingdom
| | - Alexey Dobrynin
- Seagate Technology, 1 Disc Drive, Derry BT48 0BF, United Kingdom
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MacKinnon CR, Zeissler K, Finizio S, Raabe J, Marrows CH, Mercer T, Bissell PR, Lepadatu S. Collective skyrmion motion under the influence of an additional interfacial spin-transfer torque. Sci Rep 2022; 12:10786. [PMID: 35750744 PMCID: PMC9232533 DOI: 10.1038/s41598-022-14969-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Accepted: 06/15/2022] [Indexed: 11/26/2022] Open
Abstract
Here we study the effect of an additional interfacial spin-transfer torque, as well as the well-established spin–orbit torque and bulk spin-transfer torque, on skyrmion collections—group of skyrmions dense enough that they are not isolated from one another—in ultrathin heavy metal/ferromagnetic multilayers, by comparing modelling with experimental results. Using a skyrmion collection with a range of skyrmion diameters and landscape disorder, we study the dependence of the skyrmion Hall angle on diameter and velocity, as well as the velocity as a function of diameter. We show that inclusion of the interfacial spin-transfer torque results in reduced skyrmion Hall angles, with values close to experimental results. We also show that for skyrmion collections the velocity is approximately independent of diameter, in marked contrast to the motion of isolated skyrmions, as the group of skyrmions move together at an average group velocity. Moreover, the calculated skyrmion velocities are comparable to those obtained in experiments when the interfacial spin-transfer torque is included. Our results thus show the significance of the interfacial spin-transfer torque in ultrathin magnetic multilayers, which helps to explain the low skyrmion Hall angles and velocities observed in experiment. We conclude that the interfacial spin-transfer torque should be considered in numerical modelling for reproduction of experimental results.
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Affiliation(s)
- Callum R MacKinnon
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE, UK.
| | - Katharina Zeissler
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK.,Bragg Center for Materials Research, University of Leeds, Leeds, LS2 9JT, UK
| | - Simone Finizio
- Swiss Light Source, Paul Scherrer Institut, 5232, Villigen, Switzerland
| | - Jörg Raabe
- Swiss Light Source, Paul Scherrer Institut, 5232, Villigen, Switzerland
| | - Christopher H Marrows
- School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK.,Bragg Center for Materials Research, University of Leeds, Leeds, LS2 9JT, UK
| | - Tim Mercer
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE, UK
| | - Philip R Bissell
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE, UK
| | - Serban Lepadatu
- Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston, PR1 2HE, UK.
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Bera S, Mandal SS. Length-scale independent skyrmion and meron Hall angles. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 33:115801. [PMID: 33326938 DOI: 10.1088/1361-648x/abd424] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Motivated by the recent observation (Zeissler et al 2020 Nature Commun. 11 428) of enigmatic radius-independent skyrmion Hall angle in chiral magnets, we derive skyrmion Hall angle based on the recent solution of skyrmions characterized by the sole length scale determined with the Dzyaloshinskii-Moriya interaction strength and applied magnetic field. We find that the skyrmion Hall angle is independent of input current density and the length-scale which determines the radius of a skyrmion. This is corroborated with the single length-scale dependent skyrmion profile which is the solution of the Euler equation of polar angle representing magnetization. Although the magnitude of Hall angle may change with the change of profile (shape) of the skyrmion, it remains unchanged for a particular profile. With the application of tunable current along mutually perpendicular directions, this property enables us to propose an experimental setup by which the transverse motion of a skyrmion can be restricted so that the skyrmion can only traverse longitudinally. We further find the length-scale and input-current density independent Hall angles for merons where their transverse motion will be opposite depending on whether the spin at their centers are up or down, in agreement with an experiment.
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Affiliation(s)
- Sandip Bera
- Department of Physics, Indian Institute of Technology, Kharagpur, West Bengal 721302, India
| | - Sudhansu S Mandal
- Department of Physics, Indian Institute of Technology, Kharagpur, West Bengal 721302, India
- Centre for Theoretical Studies, Indian Institute of Technology, Kharagpur, West Bengal 721302, India
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