Magnetic field effect on the complex permeability for a Mn-Zn ferrite and its composite materials

Complex permeability spectra (mu* = mu'-i mu ") in Mn-Zn ferrite and its co mposite materials have been studied in the frequency range from 10 kHz to 2 GHz under magnetic fields up to 1000 Oe. In the sintered ferrite, the mu' spectrum has a resonance type frequency dispersion above 100 kHz which is o riginated mainly by the domain wall vibration and mu " shows a maximum at a bout 800 kHz in the absence of a de magnetic field. Under de magnetic field , dispersion character changes from resonance type to relaxation type spin resonance with the disappearance of the magnetic domain wall. High frequenc y permeability can be suppressed by the skin depth effect of eddy current a bove 1 MHz. In the composite materials, the permeability dispersion frequen cies locate above 100 MHz and resonance type dispersion, which is mainly at tributed to the spin resonance, is stabilized by the demagnetizing field in the embedded particles. Spin resonance character is enhanced by the extern al dc magnetic field. (C) 1999 Elsevier Science Limited All rights reserved .