Improved magnetic properties of Zn-substituted strontium W-type hexaferrites

The Zn2+ substitution for the Fe2+ site was found to be effective for the improvement of the saturation magnetization (Ms) of strontium W-type hexaferrite (SrFe18O27). For this study, polycrystalline SrFe18O27 with various Zn-substituents of SrZnxFe(2-x)Fe16O27 (SrZnxFe(2-x)W, 0.0 ≤ x ≤ 1.5) were sintered at high temperatures in a reduced oxygen atmosphere of 10−3 atm. While pure SrZnxFe(2-x)W-type solid solutions (0.0 ≤ x ≤ 1.0) could be obtained, the second phase of ZnFe2O4 was obtained from the sample of x = 1.5, and the second phases of Sr2Zn2Fe12O22 and ZnFe2O4 was obtained from the sample of x = 2.0. With increasing x up to 1.0, Ms values were monotonously increased and the highest Ms value of 87.7 emu/g was obtainable from the sample of x = 1.0 sintered at 1250 °C. In addition, post-annealing heat treatments of samples for oxygenation at 300 °C in pure oxygen gas revealed that oxygen non-stoichiometry increased with increasing the sintering temperature, leading to the increase in Ms, unit cell volume, and electrical conductivity.