Oriented barium hexaferrite thick films grown on c-plane and m-plane sapphire substrates

The magnetic and structural properties of thick pulsed laser deposited (PLD) barium hexaferrite (BaM) films grown on c-plane and m-plane sapphire substrates were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Rutherford backscattering spectroscopy (RBS), vibrating sample magnetometry (VSM), and ferrimagnetic resonance (FMR). Previously, BaM thin films (-0.5 μm) grown on c-plane (0001) sapphire substrates exhibited magnetic properties closely approaching those of single crystal spheres. These films are potentially useful for thin film millimeter-wave devices such as circulators, isolators, and phase shifters, provided that thick films (e.g., 20 to 100 μm) with suitable magnetic and dielectric properties can be grown. In general, it was found that an increase in film thickness leads to the growth of either textured polycrystalline BaM, which can be loosely adherent, or delamination of the films. However, well oriented thick BaM films were grown up to 15 and 20 μm on the c-plane and m-plane sapphire substrates, respectively, before delamination occurred. The FMR linewidth, ΔH, was 200 Oe at 85 GHz for an annealed 15 μm thick PLD BaM film on c-plane sapphire with 4πM=4200 G, H_A=16000 Oe and an XRD ω-scan of 0.51° FWHM about the (008) BaM plane. The FMR linewidth of PLD BaM films grown on m-plane (11_00) sapphire substrates were greater than 450 Oe with 4πM-4000 G H_A=16000 Oe. the m-plane films were magnetically well oriented in the film plane with M_r/M _s along the easy axis greater than 90% for all PLD m-plane BaM films