Theory for the spin Seebeck effect in the spin-flop phase of the Heisenberg antiferromagnet RbMnF3

RbMnF3 is a cubic antiferromagnet with a very small anisotropy field, so that it can be considered a prototype of a three-dimensional Heisenberg antiferromagnet. In this paper, we present a theoretical investigation of the spin Seebeck effect (SSE) in the spin-flop phase of RbMnF3. The analysis begins with the formulation of a quantum theory for spin waves in antiferromagnetic systems exhibiting cubic anisotropy, considering both the antiferromagnetic and spin-flop phases. Subsequently, we develop a magnon diffusion theory for the SSE in antiferromagnetic materials with cubic anisotropy in the spin-flop phase. The theoretical predictions are in good agreement with the experimental data, supporting the validity of the bulk magnon diffusion theory for describing spin transport in antiferromagnetic materials in the spin-flop phase.