Frequency Dependence of Initial Permeability of Ferrites near the Onset of Low Field Loss

Measurements have been made of the initial permeability, μ=χ0+1, on a series of ferrites as a function of frequency above ωM=γ4πMs. The reciprocal of the real part of the susceptibility, 1/χ0′, was found to be linear in ω over a wide frequency range and reasonably independent of everything except ωM. This behavior is shown to be consistent with a model describing the susceptibility as an integral over a distribution of Lorentzian modes with frequencies from zero to ωM. It was also found that (χ0″)−1/2 was linear in ω over a smaller frequency range and that the initial slope and subsequent shape depends strongly on the magnitude of the intrinsic loss of the material and its frequency dependence. This behavior is also consistent with the above model.