Magnetic anisotropy due to the Rashba effect in antiferromagnets

Ieda, Junichi   ; Maekawa, Sadamichi

Recently spintronics phenomenon based on antiferromagnets has drawn much attention. In 2014, we proposed a mechanism that the Rashba spin-orbital interaction produces magnetic anisotropy due to competition with magnetic exchange interaction in a ferromagnetic thin film. This time the theory is extended to antiferromagnet with the Rashba spin-orbital interaction. Conduction electron spin that hops between the nearest neighbor sites on a lattice with antiferromagnetic order in two sublattice is considered. Two kinds of lattice models which feel an on-site exchange interaction and the Rashba interaction of (a) the same sign for the nearest neighbor hopping, or (b) the different sign for the next nearest neighbor hopping are investigated. Former is a model of the Rashba effect occurring at the interface between the antiferromagnetic thin film and another substance and the latter is for the Rashba effect in the antiferromagnet in which the inversion symmetry locally broken, such as CuMnAs. For each model, the angle dependence of the total energy on the antiferromagnetic order-parameter direction is obtained and the expression of the uniaxial magnetic anisotropy constant is derived. In model (a), it is shown that transition from easy plane anisotropy to perpendicular magnetic anisotropy occurs with increasing Rashba interaction. On the other hand, in model (b), it is shown that Rashba interaction always favors the perpendicular magnetic anisotropy as a result of competition with exchange interaction.