Orbital contribution to perpendicular magnetic anisotropy in Co80Pt20 thin films

We have measured x-ray magnetic circular dichroism spectra at the Co and Pt L-2,L-3-edges in Co80Pt20 perpendicular magnetization films, wherein the uniaxial magnetic anisotropy constant, K-u, significantly increases with decreasing film thickness, delta, and reaches 1.7x10(7) erg/cm(3) for delta=3 nm. The anisotropy of the orbital magnetic moment (AOM) was estimated as a function of delta, and the relationship between AOM and K-u is discussed. When the thickness was reduced, the AOM for Pt 5d was nearly constant, whereas a weak increase was observed for Co 3d. Both AOMs are small in contrast to the large K-u, and any proportionality between AOM and K-u was hardly recognized. This result indicates that a large AOM is not always a necessary and sufficient condition for the appearance of perpendicular magnetization.