Effect of Annealing Atmosphere on Microstructure, Magnetic, and Microwave Properties of Barium Hexaferrite Thin Films

Barium hexaferrite (BaM) has attracted more and more attention in the fields of microwave devices because of its large saturation magnetization (Ms) and high magnetocrystalline anisotropy field. In this report, highly oriented barium hexaferrite thin films were grown on Pt-coated Si substrate by sol-gel way with different annealed atmosphere. It is found that the thin film has nice properties when it is annealed in N-2 + O-2 atmosphere. It is confirmed by X-ray diffraction and atomic force microscopy that the film exhibiting strong c-axis orientation and Lotgering factor is 0.96. Magnetic hysteresis loops revealed BaM has strong sign of anisotropy with squareness ratio of 0.93, and the 4 pi Ms is 3956 Gs. Meanwhile, ferromagnetic resonance (FMR) measurement shows the FMR linewidth is as low as 125 Oe @50Ghz, and anisotropy field is 16.22 kOe. These data make sure these BaM thin films are suitable application for millimeter wave devices, for example, circulators, isolators, and filters.