Evolution of microstructure and magnetic properties in magnetron-sputtered CoCr thin films

Abstract

The microstructure and magnetic-structure development in magnetron-sputtered Co-22at%Cr thin films deposited on amorphous substrates has been examined systematically and in detail. It has been found that the initial deposit is amorphous up to a thickness of [approximate]5 nm. By 10 nm thickness, a polycrystalline highly hcp c-axis textured (out of the film plane) microstructure is observed. At 50 nm thickness, a distinct columnar morphology has developed. A distinct subgrain structure was also observed in the thinner films (10-50 nm). The magnetization is initially in-plane and retains in-plane components up to a thickness of [approximate] 50 nm, after which it is predominantly out-of-plane. The effects of in-plane film stress are reflected in the effective anisotropy field and are most evident in the thinner films, where the stress is highest. The thinnest (10 nm) films display in-plane 180[deg] domain walls while thicker (50 nm) films exhibit out-of-plane "dot"-type domain structures. The "dot" domains were observed even in films that had not yet developed a columnar morphology. Intermediate-thickness films show a "feather-like" contrast, indicating that both in- and out-of-plane magnetization components are present. Intrinsic film stress was found to play a major role in determining the preferred magnetization direction and, thus, the resulting magnetic domain configurations.