Rashba magnetic anisotropy in antiferromagnets

Ieda, Junichi   ; Maekawa, Sadamichi

We study magnetic anisotropy in antiferromagnets (AFMs) with the inversion symmetry breaking (ISB). Magnetic anisotropy determines an energy barrier that separates preferable orientations of staggered magnetization in AFMs, and in its sense, understanding and controlling the magnetic anisotropy energy (MAE) in AFMs are fundamentally important for devising magnetic memory bits that should be reliably robust against any external (thermal, magnetic field, and electric current) noises. It has also been pointed out that a large value of MAE in AFMs is advantageous for the exchange bias field that is routinely used to fix magnetization direction at the AFM/FM interface in current magnetic memory technology. In this work, we employ two representative models for the AFMs and obtain the MAE as a consequence of the cooperation of the Rashba spin-orbit (RSO) and exchange interactions. For the global ISB model the MAE shows a transition depending on the magnitude of the RSO coupling: the easy-plane magnetic anisotropy is favored with the small RSO coupling whereas the perpendicular magnetic anisotropy (PMA) is induced with the large RSO coupling. For the local ISB the PMA is generally results in, which contrasts to the corresponding ferromagnetic case in which the condition for the PMA depends on the band structure and dimensionality. These features are particularly important for stabilizing the direction of the order parameter in AMF nanostructures and for electrical-field control of the MAE via the externally modulated RSO coupling.