Site preference and magnetic properties for a perpendicular recording material: BaFe_{12-x}Zn_{x/2}Zr_{x/2}O_{19} nanoparticles

The site preference and magnetic properties of Zn-Zr substituted BaM ferrite BaFe12-xZnx/2Zrx/2O19 nanoparticles with x=0-1.6 have been studied using Mossbauer spectra and magnetic measurement. The results show that the magnetizations and magnetocrystalline anisotropies are closely related to the distributions of Zn-Zr ions on the five sites. The BaFe12-xZnx/2Zrx/2O19 nanoparticles exhibit unusual saturation magnetization, which increase at low substitutions, reach a maximum and then decrease. Massbauer spectra show that the Zn-Zr ions preferentially occupy the 2b and 4f(VI) sites. The preference for the 4f(VI) site is responsible for the anomalous increase in the magnetization at low Zn-Zr substitutions. At x greater than or equal to 1.2 the rapid decrease in the magnetizations is mainly attributed to a noncollinear magnetic structure. In addition, a monotonic decrease in the magnetocrystalline anisotropy with Zn-Zr substitutions has its origin in the preference of the Zn-Zr ions for the 2b and 4f(VI) sites.