Negative dependence of surface magnetocrystalline anisotropy energy on film thickness in Co₃₃Fe₆₇ alloy

In this work, the magnetocrystalline anisotropy energy (MAE) on the surface of Fe₃₃Co₆₇ alloy film is extracted from x-ray magnetic linear dichroism (XMLD) experiments. The result indicates that the surface MAE value is negatively correlated with thickness. Through spectrum calculations and analysis, we find that besides the thickness effect, another principal possible cause may be the shape anisotropy resulting from the presence of interface roughness. These two factors lead to different electron structures on the fermi surface with different exchange fields, which produces different spin-orbit interaction anisotropies.