Mössbauer spectra of magnetic nanoparticles in the model of continuous diffusion and precession of uniform magnetization

A formalism based on the Brown kinetic equation has been developed to describe the Mössbauer spectra of magnetic nanomaterials in the presence of a continuous relaxation process with the inclusion of the diffusion and precession of uniform magnetization in the magnetic-anisotropy field of nanoparticles. Such a generalization of the relaxation model allows not only the inclusion of physical mechanisms of the formation of the magnetic hyperfine structure that are inherent in the system of single-domain magnetic nanoparticles but also an explanation of qualitative features observed in experimental spectra, in particular, the appearance of the magnetic-nature line doublets in these spectra in addition to the standard line sextets of the ⁵⁷Fe nuclei.