2017 Fiscal Year Research-status Report
Antiferromagnetic Skyrmions
| Project/Area Number |
17K05511
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| Research Institution | Tohoku University |
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Principal Investigator |
Tretiakov Oleg 東北大学, 金属材料研究所, 助教 (50643425)
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Keywords | Antiferromagnets / Skyrmions |
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| Outline of Annual Research Achievements |
We investigated the stability and lifetime of antiferromagnetic skyrmions using analytical techniques and numerical simulations [arXiv:1709.04454, submitted to Phys. Rev. Lett. (2017)]. We have proposed a Hamiltonian dynamics formalism for the current and magnetic field driven dynamics of ferromagnetic and antiferromagnetic domain walls [Phys. Rev. B 95, 174408 (2017)]. We also studied for the first time the theory of topological spin Hall effect in antiferromagnetic skyrmions [arXiv:1709.02931, submitted to Phys Rev. Lett. (2017)].
We investigated the effect of large curvature and dipolar energy in magnetic films with periodically modulated surfaces on magnetization. We predicted that the dipolar interaction and surface curvature can produce perpendicular anisotropy which can be controlled by engineering special surfaces [Phys. Rev. Lett. 119, 077203 (2017)]. We presented an analytical theory of domain-wall tilt due to field in a nanostrip with out-of-plane anisotropy and Dzyaloshinskii-Moriya interaction. This theory treats the domain walls as 1D objects with orientation-dependent energy, which interact with the sample edges [Phys. Rev. B 96, 134417 (2017)].
We studied and quantified in details the skyrmion stability, for which we used an innovative multiscale approach to simulating spin dynamics based on LLG equation. As a key operation for devices, the process of annihilating a skyrmion by exciting it with a spin polarized current pulse was analyzed, showing that skyrmions can be reliably deleted by designing the pulse shape [Phys. Rev. B 96, 020405(R) (2017)].
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The stability and lifetime of antiferromagnetic skyrmions was addressed using analytical methods and numerical nudged elastic band thechnique [arXiv:1709.04454, submitted to Phys. Rev. Lett. (2017)]. Hamiltonian dynamics formalism was proposed for the description of current and magnetic field driven dynamics of antiferromagnetic spin textures [Phys. Rev. B 95, 174408 (2017)]. We also addressed for the first time the theory of topological spin Hall effect in antiferromagnetic skyrmions [arXiv:1709.02931, submitted to Phys Rev. Lett. (2017)].
The effect of large curvature and dipolar energy in thin magnetic films with periodically modulated surfaces was investigated and we predicted that the dipolar interaction and surface curvature can produce perpendicular anisotropy which can be controlled by engineering special periodic surfaces [Phys. Rev. Lett. 119, 077203 (2017)]. Analytical theory of domain-wall tilt due to a transverse in-plane magnetic field in a magnetic nanostrip with out-of-plane anisotropy and Dzyaloshinskii-Moriya interaction was developed [Phys. Rev. B 96, 134417 (2017)]. Furthermore, we quantified the skyrmion stability, for which we used an innovative multiscale approach to simulating spin dynamics based on the Landau-Lifshitz-Gilbert equation. As a key operation for devices, the process of annihilating a skyrmion by exciting it with a spin polarized current pulse was analyzed, showing that skyrmions can be reliably deleted by designing a pulse shape [Phys. Rev. B 96, 020405(R) (2017)].
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| Strategy for Future Research Activity |
- Formulate the problem of moving single antiferromagnetic skyrmion under the influence of spin-orbit torques in a AFM/heavy-metal bilayer. Employ the generalized Landau-Lifshitz-Gilbert equation (LLG) approach to both staggered field and magnetization dynamics to determine the effective equations of motion. Identify the main generalized coordinates of AFM skyrmion and associated with them degrees of freedom and relaxation times.
- Solve the generalized LLG equation with spin-orbit torques for antiferromagnet in a general case of large currents and temperature gradients. Identify the applicability limits of the LLG equation approach for antiferromagnetic skyrmion dynamics. Assess the effects of the Dzyaloshinskii-Moriya interactions on AFM skyrmions and their dynamics.
- Derive the coefficients of spin-orbit torques in non-uniform antiferromagnets based on underlying symmetries. Use these results to determine the drift velocity of current-driven AFM skyrmion, examine possible deviations from linear regime at high currents.
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