Bulk permittivity, low frequency relaxation and the magnetic properties of Pb(Fe½Nb½)O3 ceramics

A Pb(Fe(½)Nb(½))O(3) ceramic sample was prepared through a high temperature solid-state reaction technique. The formation of a single-phase perovskite compound was confirmed by an x-ray diffraction technique. Dielectric and impedance parameters were measured as a function of frequency (10(2)-10(6) Hz) at different temperatures (28-200 °C). The results were described using an equivalent circuit model and by extending the universal capacitor concept introduced by Jonscher. Bulk permittivity of the material and the power law exponent (extracted from impedance data) exhibits an anomaly at a particular temperature related to the ferroelectric-paraelectric transition. A slow relaxation process has been observed in the vicinity of the transition temperature. Temperature dependent magnetization (2-300 K) was measured at different magnetic fields in both zero-field-cooled (ZFC) and field-cooled (FC) modes. An antiferromagnetic transition was observed at 158 K but an unusual increase in magnetization below this transition indicates the onset of weak ferromagnetism at low temperature in this system. Nonlinear M-H and a finite opening in the hysteresis loop at 2 K substantiate the presence of ferromagnetic interactions. Significantly, a thermomagnetic history-dependent feature is observed below 9 K. The ZFC magnetization shows a sharp fall and it bifurcates from the monotonically increasing FC counterpart on decreasing temperature. This temperature, where ZFC magnetization shows a sharp peak, decreases with the increase in measurement field and it indicates the presence of a metastable magnetic state at low temperature.