Effect of negative substrate bias on the film structure and magnetic properties in sputter-deposited Co–Cr films

Abstract

Film structure and magnetic properties are investigated in Co–Cr films sputter deposited with an applied substrate bias voltage. Large grains with c-axis orientation are found at negative bias between 40 and 75 V. Coercivity decreases remarkably in these films. These changes in film structure and magnetic properties by applying low bias originate from the moderate bombardment by Ar ions under low oxygen contamination as well as little Ar incorporation. With further increase of negative bias, saturation magnetization decreases to the bulk value and perpendicular magnetic anisotropy decreases to zero, because violent ion bombardment yields complete solid solution of Co and Cr. Temperature dependence of saturation magnetization in zero bias Co–Cr films with perpendicular magnetization reveals a compositional inhomogeneity in which concentration of Cr distributes between 10 and 30 at. %. The compositional inhomogeneity is eliminated by the substrate bias.