Epitaxy barium ferrite thin films on LiTaO₃ substrate

Barium hexaferrite (BaM) thin films were deposited on (0001) LiTaO₃ substrates by pulsed laser deposition. Effects of the substrate temperature and oxygen gas pressure on the formation and quality of these films were studied. Films deposited at a substrate temperature of 800 °C and an oxygen pressure around 0.23 mbar showed the best c axis normal to the film plane with locked in-plane orientation. The saturation magnetization M_s and anisotropy field H_a measured by vibrating sample magnetometer were almost the same as those reported on bulk barium ferrite. Decreasing oxygen pressure hinders the formation of the Ba layer in BaM magnetoplumbite structure and gives rise to the spinel phase, which greatly decreases coercivity H_c of the films and finally destroys the whole BaM structure. Effects of the lattice mismatch and substrate-induced strains on the film structure were also studied. It was found that barium ferrite thin films grown on LiTaO₃ substrates tend to choose a matching mode with compressional strains rather than shear strains.