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arXiv · 1603.03736

Magnon-drag thermopower and Nernst coefficient in Fe, Co, and Ni

Sarah J. Watzman·Rembert A. Duine·Yaroslav Tserkovnyak·Stephen R. Boona·Hyungyu Jin·Arati Prakash·Yuanhua Zheng·Joseph P. Heremans
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Abstract

Magnon-drag is shown to dominate the thermopower of elemental Fe from 2 to 80 K and of elemental Co from 150 to 600 K; it is also shown to contribute to the thermopower of elemental Ni from 50 to 500 K. Two theoretical models are presented for magnon-drag thermopower. One is a hydrodynamic theory based purely on non-relativistic, Galilean, spin-preserving electron-magnon scattering. The second is based on spin-motive forces, where the thermopower results from the electric current pumped by the dynamic magnetization associated with a magnon heat flux. In spite of their very different microscopic origins, the two give similar predictions for pure metals at low temperature, allowing us to semi-quantitatively explain the observed thermopower of elemental Fe and Co without adjustable parameters. We also find that magnon-drag may contribute to the thermopower of Ni. A spin-mixing model is presented that describes the magnon-drag contribution to the Anomalous Nernst Effect in Fe, again enabling a semi-quantitative match to the experimental data without fitting parameters. Our work suggests that particle non-conserving processes may play an important role in other types of drag phenomena, and also gives a predicative theory for improving metals as thermoelectric materials.

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Sarah J. Watzman, Rembert A. Duine, Yaroslav Tserkovnyak, Stephen R. Boona, Hyungyu Jin, Arati Prakash, Yuanhua Zheng, Joseph P. Heremans. 2016-09-10. Magnon-drag thermopower and Nernst coefficient in Fe, Co, and Ni. https://doi.org/10.1103/physrevb.94.144407

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