2020 Fiscal Year Research-status Report
Deciphering spin-orbit torque in magnetic single layers: Towards spin-torque devices with extended scalability
| Project/Area Number |
20K15156
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| Research Institution | Tohoku University |
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Principal Investigator |
LAU Yongchang 東北大学, 金属材料研究所, 特任助教 (60795764)
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| Project Period (FY) |
2020-04-01 – 2022-03-31
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| Keywords | Compensated ferrimagnet / Spin-orbit torque / Spin-orbitronics / Spin caloritronics / Anomalous Nernst effect |
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| Outline of Annual Research Achievements |
Epitaxial Mn2RuxGa (MRG) films of varying Ru composition were grown on single-crystal MgO(001) substrates by magnetron co-sputtering. Magnetic compensation was achieved at 300K for sample with x ~ 0.6 and preliminary single-layer spin-orbit torque (SOT) measurements were performed on these samples. In addition, anomalous Nernst effect (ANE) was discovered in MRG. The ANE, the Seebeck effect and the transverse thermoelectric conductivity of MRG were found to switch sign across the magnetic compensation. These results suggest instead of the net moment, the direction of one magnetic sublattice moment governs the magneto-caloric properties of this compound. This work leads to 2 oral presentations (JSAP spring meeting 2021 and INTERMAG 2021) and a related manuscript is in preparation.
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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 originally planned research for FY2020 includes:
1) Optimize the growth of MRG on single-crystal substrates
2) Develop an experimental protocol for quantifying the SOT
3) Investigate the correlation between the SOT and different properties
MRG films of varying strain, magnetic compensation temperature, and ordering were successfully grown by varying the film thickness, Ru concentration, and growth temperature. SOT was quantified by harmonic Hall technique in a PPMS equipped with a home-made measurement platform. Correlation between magnetic compensation, domain twinning and SOT was the main focus. Similar comparison was extended to between magnetic compensation and anomalous Nernst effect. All initially planned research aims were achieved. The project has progressed smoothly.
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| Strategy for Future Research Activity |
Based on the knowledge acquired in FY2020, two main research activities/strategies were planned:
1) Domain twinning of MRG grown on centrosymmetric substrates (e.g. MgO) is a main technical obstacle that hinders the observation of single-layer SOT. The growth of MRG on non-centrosymmetric substrates (e.g. GaAs) will be optimized, which is expected to reduce the domain twinning.
2) The growth of a new inverse Heusler compound Mn2RuAl will be optimized. Replacing Ga by Al is expected to reduce the lattice constant, providing a better lattice match with GaAs than MRG.
These strategies will improve our understanding on single-layer SOT and eventually will guide us towards SOT switching of a magnetic single layer.
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| Causes of Carryover |
Partly due to COVID-19, part of the budget, including that originally planned for the travel expenses will be transferred to the next fiscal year. In FY2021, I plan to use the research budget for the purchase of new instruments (e.g. lock-in amplifier and a.c. current sourcemeter), sputtering targets (e.g. Mn-Al alloy target for exploring new materials), and single-crystal substrates (e.g.MgO, SrTiO3, semi-insulating GaAs, etc.). If the situation improves, part of the budget will be used for attending domestic and international conferences held in late2021/early2022.
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Research Products
(7 results)
