Effect of pre-sintering particle size on the microstructure and magnetic properties of two-step hot-press prepared BaFe12O19 thick films

Both particle size and processing conditions can affect the magnetic properties of ferrite materials. In this work, the two-step hot-press procedures (hot-press magnetic orientation followed by hot-press sintering) is designed for fabrication of high quality BaFe12O19 thick films. The effects of pre-sintering particle size (Gpre) on the microstructure and magnetic properties of the thick films are investigated. Results show that reducing Gpre increase caxis orientation and remanence ratio (RR) of sintered thick film greatly. This should be due to the reduced energy barriers for grain orientation during the hot-press magnetic orientation process. Decreasing Gpre from 920 nm to 170 nm leads to larger coercivity (Hc), while the saturation magnetization does not change notably above Gpre = 170 nm. The Hc mechanism is further analyzed by the Gpre dependent anisotropy field Hk and the first-orderreversal curves of the thick film. Results show that Hk increases with reducing Gpre, while the inter-grain interactions are not notably affected by Gpre. Therefore, the increase of Hc should be contributed by both the decrease of sintered particle size and the improved RR of the film after hot-press magnetic field orientation. The above results show that the two-step hot-press sintering prepared hexaferrite thick films with optimized Gpre is a good candidate for the realization of self-biased high frequency devices.