Compositional separation in sputtered Co-Cr films

Abstract

Compositional separation (CS) in Co-Cr based alloy thin films, which produces Co-enriched regions within grains, is expected to produce a particulate type magnetic microstructure suitable for high density magnetic recording. In order to study CS, using NMR and TEM, we investigate the influence of film thickness, bias voltage and film composition on CS for sputtered Co-Cr films and examine the occurrence of CS in Co-Ru films. For Co-22 at% Cr films, we observe that CS occurs drastically at the initial stage of film growth and continues to occur throughout film growth. We find that the degree of CS can be controlled by bias voltage. These resuks suggest that CS is a diffusion-limited phenomenon which occurs at the film surface during film growth. CS is observed to occur even in the Cr content range between 5 and 10 at%, suggesting the occurrence of compositional phase separation in an hep solid solution. The discovery of CS in Co-Ru films supports a claim that the origin of CS lies in magnetically induced phase separation.