Mossbauer spectra of noninteracting single-domain ferromagnetic particles including superparamagnetic relaxation:: Simplification of the multilevel method

A simple method of calculation of Mossbauer relaxation spectra of single-domain ferromagnetic particle assemblies is developed from Brown's model of coherent rotation of the magnetization utilizing matrix continued fractions to compute the lineshape. The method allows one to obtain a simple analytical formula for the lineshape in the strong relaxation limit, which provides results in agreement with numerical calculations and radically simplifies analysis of the spectra.