The thermal variations in electrical conductivity of polycrystaline Mn-Zn ferrites was investigated by impedance spectroscopy. Two well defined semicircles were observed in complex impedance plots, which were associated with grain (or bulk) and grain boundary impedance response, for the high and low frequency ranges, respectively. From these results, the characteristic relaxation frequencies were obtained for each process. The grain boundary frequency exhibited a monotonous behavior as a function of temperature, while the bulk frequency showed a maximum at 132 deg C. By a magnetic method, it was verified that this temperature corresponds to the Curie transition. These results show therefore that a magnetic phase transition can be studied by means of electrical methds.
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