Permeability and losses in ferrites from dc to the microwave regime

Fluxmetric and transmission line methods have been combined in the wideband characterization of Mn–Zn and Ni–Zn soft ferrites. The real μ′(f) and imaginary μ″(f) permeability components and the energy loss W(Jp,f) have been obtained in ring samples, for defined values of the peak polarization Jp up to 1 GHz. The role of an increasing dc magnetic field 0≤Hdc⊥≤140 kA/m transverse to the ring plane on the frequency dependence of μ′(f), μ″(f), and W(Jp,f) has also been investigated. Permeability and energy losses are interpreted applying the statistical theory of losses to the case where spin damping is the leading cause of the magnetic energy dissipation. The separate roles of domain wall processes and rotations are consequently put in evidence and predicted by associating them to relaxation and ferromagnetic resonance effects, respectively. The rotational susceptibility is obtained, as a solution of the linear Landau–Lifshitz–Gilbert equation, averaged over a distribution of effective anisotropy fields and the loss is calculated accordingly.