Properties of Ba-hexaferrite thin films with different thicknesses

M-type Ba-hexaferrite (BaM) thin films with different thicknesses were deposited on (0 0 1) Al2O3 substrates by RF magnetron sputtering. Effects of film thickness on the crystallographic, morphological and magnetic properties were investigated. Experimental results showed that properties of BaM thin films are strongly dependent on thickness and thinner film favors to obtain better (0 0 l) planes orientation with narrower XRD FWHM. The 150-nm thick film possesses columnar-type grains having c-axis orientation perpendicular to the film plane. However, with the thickness increasing from 150 to 550 nm, acicular-type grain increases. Thus, the texture of (0 0 l) planes orientation of the film deteriorates; the saturation magnetization and perpendicular magnetocrystalline anisotropy also decrease gradually. Mechanisms for these variations are attributed to the increase of random nucleation sites and strain relaxation in the films with increasing thickness.