Effects of Pt and Ta on the magnetic anisotropy of Co and Co–Cr thin films

Abstract

We have investigated the magnetic anisotropy energy (MAE) of binary Co–X (X=Cr, Ta, Pt) and ternary Co–Cr with Ta or Pt. It is found that Cr considerably decreases the MAE of Co, and a severer reduction of the MAE has been found in Co–Ta and Co–Cr–Ta within an extremely low solubility limit of Ta less than a few atomic percent. In contrast, Pt gives no noticeable change in the MAE of Co, but causes remarkable enhancement of the saturation magnetization and the MAE of Co–Cr alloy. These enhancement can be explained by the reduction of the Cr content due to Pt in ferromagnetic Co-enriched regions in a segregated phase. A thermodynamical consideration taking into account the magnetic term of Gibbs free energy gives a qualitative explanation for the role of Pt.