Energy Losses in Soft Magnets from DC to Radiofrequencies: Theory and Experiment

Abstract

We summarize the phenomenology of energy losses in soft magnetic materials from quasi-static behavior to radiofrequency regimes. We show that an encompassing interpretative framework can be worked out by applying, under very general terms, the statistical theory of losses and the associated concept of loss separation. By this theory one can account for the dissipation phenomena both in metallic alloys, where they derive from the Joule effect, and in nearly insulating soft ferrites, where spin damping in the ferromagnetic precession is assumed to dominate. In all cases we distinguish between the viscous motion of the domain walls, having pure relaxation character, and the damped rotation of the spins inside the magnetic domains, which in ferrites is associated with ferromagnetic resonance and is described through the Landau–Lifshitz–Gilbert equation. These concepts are successfully applied, in particular, to the quantitative description of the frequency dependence of permeability and losses in amorphous Co-based alloys and sintered Mn–Zn and Ni–Zn ferrites, experimentally determined up to 1 GHz.