Effect of Bi2O3, MnCO3 additives on the structure and magnetic properties of M-type Sr-hexaferrites

The effects of additives Bi2O3 and MnCO3 on the structural and magnetic properties of M-type Sr-hexaferrites (SrFe12O19) prepared by a conventional solid-state reaction method were studied. The saturation magnetization value of undoped SrFe12O19 is 71.8 emu/g; it increases to 72.6 emu/g and 74.2 emu/g with Bi2O3 doping of 0.5 wt% and 1.0 wt%, respectively. However, abnormal grain growth occurs and the coercivity (H-C) decreases significantly in the 1 wt% Bi2O3-doped sample. Co-doping of 0.5 wt% Bi2O3 + 0.5 wt% MnCO3 is effective, because a higher saturation magnetization (73.1 emu/g) than that of undoped SrFe12O19 could be achieved with a relatively large coercivity of similar to 3.3 kOe. Based on the lattice parameter calculation, Bi-3+ preferably substitutes into Fe3+ sites rather than Sr2+ sites in M-type Sr-hexaferrite. The enhanced saturation magnetization can be attributed to the selective substitution of nonmagnetic Bi3+ into the down-spin Fe3+ site (4f(1) or 4f(2)).