Abstract
We present a general approach to magnetic losses in Mn-Zn ferrites and apply it to broadband (DC –1 GHz) measurements performed on different types of sintered ring samples. The separate contributions of rotations and domain wall displacements to the magnetization process and the associated dissipation mechanisms are recognized and treated under the concept of loss decomposition, where hysteresis, excess, and classical components are separately identified. By investigating the role of sample size, the eddy current losses are singled out and calculated by means of a variational multiscale approach, taking into account the heterogeneous structure of the material. In sufficiently small samples, spin damping becomes the sole relevant dissipation channel. When involving the spin precession inside the moving domain walls, it gives rise to the hysteresis and excess loss components. The frequency dispersion of the domain wall susceptibility, experimentally separated from the rotational susceptibility, is consistent with a relaxation process, with no resonances involved. Beyond a few MHz, only rotations inside the domains survive and the associated losses are described via the Landau–Lifshitz–Gilbert equation for spin dynamics, with distributed effective anisotropy fields.
