Frequency dispersion of complex permeability in Mn–Zn and Ni–Zn spinel ferrites and their composite materials

Complex permeability spectra μ*=μ′−iμ″ for two types of spinel ferrites (Ni–Zn ferrite and Mn–Zn ferrite) and their composite materials have been investigated. The contribution of domain-wall and natural resonance to the permeability spectra was estimated by the numerical fitting of actual measurement data to a simple formula. Frequency dispersion type of each component, relaxation or resonance, can be estimated from one of the fitting parameters, damping factor. In sintered Mn–Zn ferrite, domain-wall contribution is dominant and gyromagnetic spin resonance or relaxation-type magnetization rotation is large in Ni–Zn ferrite. However, relaxation character is dominant in both Mn–Zn and Ni–Zn ferrite composite materials. In composite materials, the permeability value can be scaled by the ferrite particle content using a simple model concerning demagnetizing field. This analysis is useful in designing the permeability spectra of ferrite composite materials.