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

•The relative content of SrFe12O19 and α-Fe2O3 was changed by multiple methods.•The irreversible susceptibilities exhibited the double-peak behavior.•The coercivities mechanism was deeply revealed.

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.

Graphical abstractThe irreversible susceptibilities χirr (H) exhibited the double-peak behavior which can be assigned to the cation vacancies in SrFe12O19. The coercivities Hc of all samples almost changed linearly with the average value Hirr of irreversible fields (peak position of χirr), indicating that the coercivity was mainly determined by the amount and distribution of cation vacancies in SrFe12O19.Figure optionsDownload full-size imageDownload as PowerPoint slide