2017 Fiscal Year Annual Research Report
Efficient Thermal Spin Conversion in Spin-spiral Systems
Publicly Offered Research
| Project Area | nano spin conversion science |
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| Project/Area Number |
17H05173
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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 – 2019-03-31
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| Keywords | Spin spiral textures / Curvature effects / Thermal gradients / Spin-orbit interaction |
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| Outline of Annual Research Achievements |
We investigated the effect of large curvature and dipolar energy in thin ferromagnetic films with periodically modulated top and bottom surfaces on magnetization behavior. We predicted that the dipolar interaction and surface curvature can produce perpendicular anisotropy which can be controlled by engineering special types of periodic surface structures [Phys. Rev. Lett. 119, 077203 (2017)]. We have proposed a Hamiltonian dynamics formalism for the current and magnetic field driven dynamics of ferromagnetic and antiferromagnetic domain walls in one-dimensional systems [Phys. Rev. B 95, 174408 (2017)]. Based on this formalism, we predicted an orientation switch mechanism for antiferromagnetic domain walls which can be tested with the recently discovered Neel spin-orbit torques.
We presented an analytical theory of domain-wall tilt due to a transverse in-plane magnetic field in a ferromagnetic nanostrip with out-of-plane anisotropy and Dzyaloshinskii-Moriya interaction. This theory treats the domain walls as one-dimensional 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 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 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 mutual effect on magnetization behavior of large curvature and dipolar energy in thin ferromagnetic films with periodically modulated surfaces was analyzed [Phys. Rev. Lett. 119, 077203 (2017)]. We predicted that the dipolar interaction and surface curvature can produce perpendicular anisotropy which can be controlled by engineering special types of periodic surfaces. We also have proposed a Hamiltonian dynamics formalism for the current and magnetic field driven dynamics of ferromagnetic and antiferromagnetic spin textures [Phys. Rev. B 95, 174408 (2017)]. Furthermore, we presented an analytical theory of domain-wall tilt due to a transverse in-plane magnetic field in a ferromagnetic nanostrip with out-of-plane anisotropy and Dzyaloshinskii-Moriya interaction [Phys. Rev. B 96, 134417 (2017)]. The prior knowledge allowed us to quantify the skyrmion stability, for which we used an innovative multiscale approach to simulating spin dynamics based on the Landau-Lifshitz-Gilbert equation [Phys. Rev. B, 96, 020405(R) (2017)].
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| Strategy for Future Research Activity |
- Formulate the problem in the language of a stochastic equation (with thermal space-dependent noise) for the magnetization dynamics in a general nanostructure with Dzyaloshinskii-Moriya interaction and curvature. Identify soft modes of magnetization and their relaxation times. It will be based on the generalized LLG equation approach to the spin spiral dynamics derived earlier by the PI.
- Solve the extended LLG equation with temperature gradients in a general case of large gradients and Dzyaloshinskii-Moriya interaction. Identify the applicability limits of the LLG equation approach with stochastic noise terms. Assess the temperature effects on spin spiral textures and their dynamics. The parts of this task, which will be overly challenging to obtain analytically due to possible nonlinear character of the equations involved, will be done numerically to construct a qualitative picture of the phenomena.
- Derive and solve the system of coupled equations for the stochastic dynamics of particular simple spin spiral configurations driven by a temperature gradient. Use these solutions to determine the figure of merit for the efficiency of heat to spin conversion.
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