M-type Ba-hexaferrite (BaM) thin films with two different structures (single layered and double layered) were deposited on (001) Al2O3 substrates by RF magnetron sputtering. The changes in microstructural and magnetic properties of the films corresponding to different layer structures and substrate temperatures (Ts) were investigated. Experimental results indicated that for the single layered films deposited directly on substrates at Ts = 300 °C and Ts = 500 °C, most of the grains are acicular type grains with their c-axis in-plane and/or randomly oriented. However, in the double layered film with first interfacial layer deposited at Ts = 300 °C and second layer deposited at Ts = 500 °C, good crystallographic characteristics and excellent perpendicular c-axis orientation were obtained. The c-axis dispersion angle (Δθc) decreased to 0.49°, while the squareness ratio and coercivity of the out-of-plane respectively increased to 0.85 and 4.67 kOe in the double layered film. The mechanism for improving perpendicular c-axis orientation with the interfacial BaM layer was attributed to an increase in the perpendicularly oriented nucleation sites and the release of the stress that comes from the film-substrate interface.

Multilayer films exhibit high saturation magnetization, high permeability, and high cutoff frequency fr, applying to magnetic inductors that satisfy both high frequency, miniaturization, and integration. In this work, we fabricate Fe/Ni81Fe19/Fe (t/100/t nm) multilayer films on Si (100) using electron beam evaporation, and investigate the Fe thickness dependence of surface morphology, saturation magnetization, coercivity, and ferromagnetic resonance fr. The results demonstrate that Fe/Ni81Fe19/Fe (4/100/4 nm) multilayer film possess relatively high saturation magnetization (12.1 kGs), low coercivity (3.1 Oe), and high ferromagnetic resonance fr (1.93 GHz).