Frequency dispersion and temperature variation of complex permeability of Ni-Zn ferrite composite materials

Permeability spectra in Ni-Zn ferrite composite materials were studied at the volume loading of ferrite above 30% and at temperatures from 100 to 400 K. The permeability decreased with decreases in the volume loading of ferrite. This decrease was much larger than that expected from the empirical mixing law. This was attributed to the demagnetizing field, generated by the magnetic poles on the surface of the ferrite particles. Simultaneously, the demagnetizing field increased spin resonance frequency. For the sintered ferrite, the primary peak of the permeability was just below the Curie temperature. The peak becomes obscure and disappeared as the volume loading decreased. The temperature dependence of the spin resonance frequency was lower in the ferrite composite material than that in the sintered ferrite. These features were also discussed from the view point of the demagnetizing field.