Effects of Al and Ca ions co-doping on magnetic properties of M-type strontium ferrites

M-type strontium ferrite is a kind of magnetic functional material with wide application prospect. In this work, SrFe12−xAlxO19 (0 ≤ x ≤ 1) and Sr1−yCayFe8Al4O19 (0 ≤ y ≤ 0.4) have been prepared by a hydrothermal method, and the effects of Al3+ doping and Al3+ and Ca2+ co-doping on the magnetic properties have been investigated. X-ray diffraction analysis indicates all the samples are a hexagonal structure, and the shift of the diffraction peaks suggests that Al3+ and Ca2+ are successfully doped in SrFe12O19. Field emission scanning electron microscope images show the particles have the hexagonal shape with the size of 1.1–2.9 µm. Vibrating sample magnetometer reveals that the doping of Al3+ and the co-doping Al3+ and Ca2+ can enhance magnetic properties of strontium ferrite. For example, the values of coercivity and the saturation magnetization of SrFe8Al4O19 are 914.1 Oe and 44.0 emu/g, which are 3% and 117% enhancement compared with SrFe12O19, respectively. For Sr1−yCayFe8Al4O19, coercivity and saturation magnetization increase from 914.1 Oe and 41.8 emu/g to 1047.2 Oe and 50.2 emu/g when the Ca2+ doping concentration increases from 0 to 0.4. Moreover, the effects of acid washing also on phase composition, morphology and magnetism are researched. The as-synthesized doping strontium ferrite will be useful for the applications in security switching and recording media.