La-Co Pair Substituted Strontium Ferrite Films With Perpendicular Magnetization

La-Co pair substitution is proposed to be an effective way to improve the magnetic properties of strontium ferrite films. Based on ab initio simulations, the structure parameters and magnetic performance of La-Co pair substituted Sr-M (SrFe₁₂O₁₉) are investigated. La-Co pair substituted Sr-M (Sr_1-xLa_xFe_12-yCo_yO₁₉) thin films with perpendicular magnetic anisotropy were also deposited on fused quartz and single-crystal Al₂O₃(001) substrates by radio frequency magnetron sputtering. The structure and crystallographic changes were analyzed by using the X-ray diffraction patterns and the morphology was evaluated from the atomic force microscope images. The magnetic characteristics were measured using a physical property measurement system. The experimental results and calculations show that: 1) the lowest energy configuration of La (Sr) Co (2a) is that Co atoms substituted at 2a site of Fe atoms, and shows the same magnetic moment as the 4f1, 4f2, 12k sites; 2) the increment of Co substitution amount to a certain extent will lead more Co²⁺ (3 μ_B) preferentially occupy Fe³⁺ (5 μ_B) in the 4f2 site, which results in significant decrease in the antiparallel magnetic moment than the parallel; and 3) the coercivity of Sr-M films could be enhanced by the Co substitution for the 2a and 4f2 sites of Fe.