Abstract: The characteristics of (Ni_0.4Zn_0.6)Fe₂O₄ spinel ferrites doped with various amount of (Ni_0.8Zn_0.2)O halite additives were investigated.
The permeability frequency spectra of the doped ferrites (1-x)(Ni_0.4Zn_0.6)Fe₂O₄+x(Ni_0.8Zn_0.2)O exhibit an anomalous transition at x=0.05, which can
be well described by the magnetic circuit model developed by Johnson and Visser. From the experimental data of X-ray diffraction, bulk density, dc electrical
resistivity, and permeability temperature spectra, the crystallographic structure of the doped ferrite for x≤0.05 is a pure spinel phase,
the presence of a small amount of oxygen vacancies in spinel lattice favors the grain growth and promotes the densification. For x>0.05, the crystallographic
structure is a diphasic mixture. The segregation of nonmagnetic y<0.8 (Ni_yZn_1-y)O halite second phase on grain boundary hinders the spinel grain growth and lowers the densification.

Key words: halite, spinel, ferrite, microstructure, electrical and magnetic properties