Ferromagnetic Resonance Porosity Linewidth Theory in Polycrystalline Insulators

TLDR: In this paper, the demagnetization fields arising from the pores between polycrystalline samples are used to explain the dipole narrowing of the linewidth of the anisotropy energy axes from crystallite to crystallite.

Abstract: Two sources of ferromagnetic resonance linewidth in polycrystalline samples which are absent in single‐crystal samples are: (1) the variation in resonant frequencies of the individual crystallites due to the random orientation of the anisotropy energy axes from crystallite to crystallite, and (2) the demagnetization fields arising from the pores between the crystallites. A theory is developed which explains this second contribution to the linewidth in terms of the two‐magnon scattering induced by the demagnetization fields of the pores. Agreement of the theoretical results with experiments is good.The present theory takes into account the dipole narrowing of the linewidth, whereas the previous independent grain theory of Schlomann does not. A second previous theory by Geschwind and Clogston makes an essential mathematical approximation, while the present theory is based on a physical model.