Effect of zinc concentration on the microstructure and relaxation frequency of Mn-Zn ferrites synthesized by solid state reaction

Mn3Zn polycrystalline ferrites with Mn1−xZnxFe2O4 stoichiometry (x=0.59, 0.61, 0.65) were prepared by solid state reaction. These ferrites were heated at different temperatures. The cubic structure with space group Fd3m (Oh7) No. 227 was confirmed by the refinement of x-ray diffraction (XRD) powders through Rietveld´s method using fullprof. Scanning electron microscopy (SEM) results revealed for all compounds a non-homogeneous grain size and shape distribution, with a mean grain size of 9 μm. The Curie temperature Tc was found to decrease as the Zn concentration increases. The magnetic domain relaxation was investigated by inductance spectroscopy (IS). The relaxation frequency fr shows an increase with the increase of the grain size while the initial permeability µi decreased. We propose an RpLp parallel arm equivalent circuit to model the IS results. The theoretical approximation is in agreement with the experimental results. We found that Mn-Zn ferrites with zinc concentration at x=0.59 and heated to 1300 °C during 6 h show a slight improvement of the homogeneous microstructure and a relatively higher relaxation frequency without the abrupt degradation of their permeability. This result suggests that ferrites treated in the manner presented in this paper are good candidates for high frequency applications.