Effects of vacancy and exchange-coupling between grains on magnetic properties of SrFe12O19 and α-Fe2O3 composites

All samples were synthesized via supercritical (390 °C) and low-temperature (190 °C) hydrothermal methods followed by annealing at 1000 °C, and contained both SrFe12O19 and α-Fe2O3 phases as reported in literature. The magnetic properties sensitively depended on the relative content of each phase, which was generally attributed to phase homogeneity and microstructural characteristics in literature as far as we know. In this paper, we observed a double-peak behavior in the curve of irreversible susceptibilities χirr versus an external magnetic field H, which was assigned to the cation vacancies and their distribution. The coercivity of the sample almost changed linearly with the average value of magnetic fields at which the χirr (H) peak located. Therefore, we conclude that the magnetic parameters, at least the coercivity, are mainly determined by cation vacancies which have usually been neglected before in SrFe12O19.