Micromagnetic study of spin transport in easy-plane antiferromagnetic insulators

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Verena Brehm, Olena Gomonay, Serban Lepadatu, Mathias Kläui, Jairo Sinova, Arne Brataas, Alireza Qaiumzadeh


Magnon eigenmodes in easy-plane antiferromagnetic insulators are linearly polarized and are not expected to carry any net spin angular momentum. Motivated by recent nonlocal spin transport experiments in the easy-plane phase of hematite, we perform a series of micromagnetic simulations in a nonlocal geometry at finite temperatures. We show that by tuning an external magnetic field, we can control the magnon eigenmodes and the polarization of the spin transport signal in these systems. We argue that a coherent beating oscillation between two orthogonal linearly polarized magnon eigenmodes is the mechanism responsible for finite spin transport in easy-plane antiferromagnetic insulators. The sign of the detected spin signal is also naturally explained by the proposed coherent beating mechanism. Our finding opens a path for on-demand control of the spin signal in a large class of easy-plane antiferromagnetic insulators.

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Interesting submission. But why eigen-modes in an easy-plane antiferromagnet is not simply a Bogoliubov sound  - a linearly dispersing magnon - possibly gapped out by an additional anistoropy and/or external fields. I am working on a similar problem and am curious how to get more than one mode in an antoferromagnet. Thanks


Two-sublattice AFMs have two magnon eigen modes. In the uniaxial easy-axis case these two eigenmodes are circularly polarized and degenerate in the absence of DMI and magnetic field. In the uniaxial hard-axis case, i.e., the easy-plane case, these two modes are linearly polarized and they are not anymore degenerate: the in-plane mode is gapless (sound-like dispersion) and the out-of-plane mode is gapped.

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