2015 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 |
15H01009
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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) |
2015-04-01 – 2017-03-31
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| Keywords | spin spiral textures / curvature effects / thermal effects / Spin-orbit interaction |
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| Outline of Annual Research Achievements |
We presented an analytic study of domain-wall statics and dynamics in ferromagnetic nanotubes with spin-orbit-induced Dzyaloshinskii-Moriya interaction (DMI) [Phys. Rev. B 93, 054418 (2016)]. We shown that even at the level of statics, dramatic effects arise from the interplay of space curvature and DMI: the domains become chirally twisted, leading to more compact domain walls. The dynamics of these chiral structures exhibits several interesting features. Under weak applied currents, they propagate without distortion. The dynamical response is further enriched by the application of an external magnetic field: the domain-wall velocity becomes chirality dependent and can be significantly increased by varying the DMI. These characteristics allow for enhanced control of domain-wall motion in nanotubes with DMI, increasing their potential as information carriers in future logic and storage devices.
We studied spin-dependent thermoelectrics based on the two-current model in metallic magnets as well as the spin Seebeck and Peltier effects that are based on spin wave excitations in ferromagnets. We derive expressions for the efficiency and figure of merit ZT of several spin caloritronic devices [IEEE Transactions on Magnetics 51, 0800414 (2015)].
We studied Skyrmion textures in antiferromagnetic materials [J. Barker and O. A. Tretiakov, Phys. Rev. Lett. 116, 147203 (2016)]. We have found that the DMI and composite nature of antiferromagnetic Skyrmions gives rise to different dynamical behavior due to both an applied current and temperature effects.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The generalized equations for the staggered field and magnetization dynamics, we derived earlier, allowed us to study efficiently the current driven and temperature driven motion of skyrmionic spin spiral textures in ferromagnets [Physical Review B 93, 064428 (2016)] and antiferromagnets [Physical Review Letters 116, 147203 (2016)]. We also studied for the first time stability and thermal properties of antiferromagnetic skyrmions. Moreover, we derive expressions for the efficiency and figure of merit ZT of several spin caloritronic devices [IEEE Transactions on Magnetics 51, 0800414 (2015)]. The prior knowledge let us analyze the effect of the electric-field controlled DMI leading to spin spirals on the pinning of domain walls in ferromagnetic nanostrips [Applied Physics Letters 108, 122403 (2016)].
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| Strategy for Future Research Activity |
- Address the Landau-Lifshitz-Gilbert equation (LLG) with colored noise. This is important for spin current generation in high temperature gradients and for highly non-equilibrium spin current propagation. Formulating and delivering the messages to the experimental community.
- Advanced considerations of combined effects of surface curvature of ferromagnetic films, Dzyaloshinskii-Moriya interaction, electric currents, and temperature. Effect on engineering a programmable out-of-plane anisotropy. Comparison of obtained analytical results for simpler cases with the stochastic micromagnetic simulations of the same spin spiral structures.
- Investigate the possibility to reformulate the problem in terms of Fokker-Planck equation which is equivalent to Langevin LLG dynamics. Similar problem has been studied by the PI [Tretiakov et al., Phys. Rev. B 71, 165326 (2005)] but not for a spin system. It requires representation of the LLG equation in the form of Master equation.
- Atomistic stochastic simulations to include the effect of ferromagnet/heavy metal interface on the spin current generation in spin spiral ferromagnets. Most of simulations will be performed on a workstation in our group, while the more computationally challenging part will be performed on the supercomputing facility of Tohoku University.
- Make analytical estimates and perform simulations to find optimal parameters for the most efficient spin conversion and propagation in spin spiral structures, such as DMI constant, thermal gradient profile, mechanical vibration frequency.
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[Journal Article] Spin Seebeck Power Conversion2015
Author(s)
A. B. Cahaya, Oleg A. Tretiakov, and G. E. W. Bauer
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Journal Title
IEEE Transactions on Magnetics
Volume: 51
Pages: 0800414-1-14
DOI
Peer Reviewed / Int'l Joint Research / Acknowledgement Compliant
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[Presentation] Antiferromagnetic Skyrmions2015
Author(s)
Oleg A. Tretiakov
Organizer
Condensed Matter Theory Seminar
Place of Presentation
University of Cologne, Cologne, Germany
Year and Date
2015-07-11
Int'l Joint Research / Invited
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[Presentation] Antiferromagnetic Skyrmions2015
Author(s)
Oleg A. Tretiakov
Organizer
International workshop on New Perspectives in Spintronic and Mesoscopic Physics (NPSMP2015)
Place of Presentation
ISSP, University of Tokyo, Kashiwa, Japan
Year and Date
2015-06-01 – 2015-06-19
Int'l Joint Research / Invited
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