Synthesis of FeNi₃/(Ni_0.5Zn_0.5)Fe ₂O₄ nanocomposite and its high frequency complex permeability

FeNi₃/(Ni_0.5Zn_0.5)Fe₂O ₄ nanocomposite particles were successfully synthesized using the hydrazine reduction combined with ammonia co-precipitation ferrite coating method. The x-ray and transmission electron microscopy analysis showed that face-centred cubic-structured FeNi₃ nanoparticles were coated with spinel Ni-Zn ferrite. The composite particles were nearly spherical with diameters of about 80-200nm and exhibited typical soft magnetic properties. The saturation magnetization (M_s) of the composite was greatly improved, compared with that of traditional ferrite. With increasing ferrite content, the eddy-current loss was effectively suppressed and a notable high frequency characteristic, in which the real part μ′ of the permeability was almost independent of the frequency, was observed. The imaginary part μ′′ remained at an extremely low value below the frequency of 300MHz. The cut-off frequency f_r was estimated to be above 1GHz. The highest value of μ′ reached 13 when the ratio of FeNi₃ to Ni_0.5Zn_0.5Fe₂O₄ was 1:1. Two peaks were observed in the permeability spectra, which may be ascribed to the ferromagnetic resonances of FeNi₃ and Ni-Zn ferrite respectively.