Spin-orbital coupling induced four-fold anisotropy distribution during spin reorientation in ultrathin Co/Pt multilayers

In this work, we synthesized (Co(t)/Pt)₃ multilayers and quantitatively determined thickness and temperature dependence of spin reorientation transition (SRT) and perpendicular magnetic anisotropy (PMA) using ferromagnetic resonance measurement. The critical thickness for PMA switching as well as tremendous magnetic anisotropy change up to 645 Oe once the temperature varies from 25 °C to -153 °C are demonstrated. More interestingly, a four-fold symmetry of magnetic anisotropy was found to be prominent during the SRT. By conducting magnetic simulation with involving high order energy term, we highly related this phenomenon to the strong spin-orbital coupling, which is considered to be the major energy term to tip the balance between the surface anisotropy and shape anisotropy. These results provide an opportunity for better understanding the transition behaviors which is essential for PMA structure preparation and their related devices.