DIELECTRIC-RELAXATION AND HOPPING OF ELECTRONS IN ERFE2O4

We report the frequency and the temperature dependence of the dielectric constant of polycrystalline ErFe2O4-delta with different degrees of oxygen deficiency delta. A large dielectric relaxation, with the order of magnitude of 10(4) and nearly of the Debye type, is observed in the magnetically ordered states within the temperature and frequency ranges of 150 K to 290 K and 1 kHz to 3 MHz, respectively. The dispersion is larger in the sample with more oxygen deficiency. From the temperature dependence of the characteristic frequency, we conclude that the elementary process of the dispersion is related to electron hopping between Fe2+ and Fe3+ ions. A large value of the dielectric constant is consistent with the existence of spontaneous polarization in the magnetic phases of this oxide. We propose that the motion of the polarization domain boundaries is a determining factor of low-frequency dielectric constant.