Managing magnon transport properties in bulk magnetic oxides within mesoscopic Boltzmann methods*

The bulk transport properties of magnon in magnetic oxides layers demand precise physical understanding of magnon diffusion,scattering and relaxation processes. In this work, we invent a novel magnon Boltzmann equation from full quantum magnon Hamiltonian. With changing thickness of magnetic oxide film(YIG), our numerical results on magnon accumulation and current shows there are two different processes in bulk magnon transport: diffusion region and relaxation region. Furthermore, we theoretically discover physical origin for decreasing of magnon diffusion length with increasing magnetic field H, it was olny observed in preivous experimental works. And since magnon relaxation closely related to many magnons scattering, a new spatial dependent draft field was introduced, similar to anisotropy, which was describing collective local motion of magnon. More importantly, our results show magnon current can be manipulated by varying of anisotropy in magnetic oxides, especially in strong anisotropic energy materials, such as NiFe₂O₄ or CoFe₂O₄. In this framework, we also provide the methods to adjust the magnon transport with applying gradient magnetic field and gradient T field.