Integral absorption of microwave power by random-anisotropy magnets

Abstract

We study analytically, within a continuous field model, and numerically, on lattices containing ${10}^{5}$ spins, the integral absorption of microwaves by a random-anisotropy magnet, $\ensuremath{\int}d\ensuremath{\omega}P(\ensuremath{\omega})$. It scales as ${D}_{R}^{2}/J$ on the random-anisotropy strength ${D}_{R}$ and the strength of the ferromagnetic exchange $J$ in low-anisotropy amorphous magnetic materials. At high anisotropy and in low-anisotropy materials sintered from sufficiently large ferromagnetic grains, the integral power scales linearly on ${D}_{R}$. The maximum bandwidth, combined with the maximum absorption power, is achieved when the amorphous structure factor, or grain size, is of the order of the domain wall thickness in a conventional ferromagnet that is of the order of ${(J/{D}_{R})}^{1/2}$ lattice spacings.