Spin-reorientation transitions in ultrathin Co films on Pt(111) and Pd(111) single-crystal substrates

Abstract

Spin-reorientation transition (SRT) behaviors in ultrathin Co films grown on both Pt(111) and Pd(111) single-crystal substrates are investigated with in situ magneto-optical Kerr effects. At the region of SRT from the perpendicular to in-plane magnetization with the increasing of Co thickness, canted out-of-plane orientations are observed, from which we can determine not only the effective second- ${(K}_{2})$ but also fourth- ${(K}_{4})$ order anisotropy constants. Both the constants, which can be separated into bulk ${K}_{2b(4b)}$ and interface anisotropy terms ${K}_{2s(4s)}$ are essential to understand the stable canted out-of-plane magnetization. We found that the value of ${K}_{2s}$ for Co/Pt(111) is larger than that for Co/Pd (111), resulting in the later onset thickness and wider range of the observed SRT, while the negative small values of ${K}_{4s}$ in the both systems yield the stable canted phases. In addition, we observed different polarization effects of Pd and Pt near the interfaces which might also contribute the contrasting SRT behaviors.