2017 Fiscal Year Research-status Report
Quantitative calculation of magnon transport properties of insulators
| Project/Area Number |
17K14102
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| Research Institution | Tohoku University |
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Principal Investigator |
Barker Joseph 東北大学, 金属材料研究所, 特任助教 (10746910)
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| Project Period (FY) |
2017-04-01 – 2019-03-31
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| Keywords | spintronics / magnons / conductivity / transport / simulation |
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| Outline of Annual Research Achievements |
I have successfully implemented the spin dynamics thermostat with quantum statistics. Comparing the results to analytic calculations shows an excellent agreement. I have also compared to experimental measurements of Yttrium Iron Garnet (YIG), where the spin model is parameterized from neutron scattering data. Calculations of the magnon heat capacity and magnetization as a function of temperature show excellent quantitative agreement, except close to the Curie temperature where there is some deviation. My calculations show the magnon heat capacity is higher at room temperature than previous estimates by 1 order of magnitude.
I have also implemented the Kubo-Green formula for calculating the magnon spin conductivity. Calculations of this quantity in YIG (for small fields) show excellent agreement with experimental measurements [Cornelissen et al. Phys. Rev. B 94 180402 (2016)]. Performing simulations using applied fields shows the suppression of the magnon spin conductivity-something which has not been measured experimentally. The implementation of the magnon thermal conductivity is basically complete and is currently undergoing testing and comparison to estimates from theory.
I have also had discussions with experimental groups leading to joint works in this area. I have been part of a joint project with the group of Eiji Saitoh where they have measured the spin transport through the antiferromagnetic insulator Cr2O3. The work is accepted for publication in Nature Materials.
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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 essential work has been completed for calculating the magnon transport properties of materials. The code is general so the method can be applied to any materials of interest. The calculations have been performed for YIG and show good agreement with experiment. The results are currently being written for publication. A little more work needs to be done to calculate the magnon heat conductivity, but this is almost complete.
One paper has been accepted for publication (Spin colossal magnetoresistance in an antiferromagnet - Nature Materials). Two more are in preparation on the topics of: quantum statistic in spin dynamics and calculations of magnon conductivities in Yttrium Iron Garnet.
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| Strategy for Future Research Activity |
In the next year of the research project I will include phonons into the simulation to see how magnon phonon interactions affect the transport properties. This will involve programming molecular dynamics alongside the spin dynamics. I expect the parameterization of this model to be challenging and it may be needed to use a simplified approach to start with until more detailed data is available.
I also plan to perform the magnon conductivity calculations for the material Gadolinium Iron Garnet (GdIG). In collaboration with the Walter Meissner Institute we have measured the non-local magnon transport but we cannot understand the results well without knowing the magnetic field dependence of the conductivities.
Results obtained so far will be presented at the PASPS10 conference in Linz, Austria August 2018 and CECAM Workshop, Lausanne, Switzerland, November, 2018. Both are invited talks.
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| Causes of Carryover |
A relatively small amount of budget is remaining for the second year which will be used primarily to present my results at conferences.
Currently these are the PASPS10 and CECAM Workshop. I expect other opportunities for invited talks will arise as well as research collaboration visits. I also hope to attend the Japanese Applied Physics conference in the autumn.
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Research Products
(2 results)
