Among magnetic thin films with perpendicular magnetic anisotropy (PMA), L10-ordered FePt has attracted significant attention because of its exceptionally strong PMA. However, the microscopic origin of its strong PMA has not been elucidated experimentally. We have investigated the contribution of the Fe 3d electrons to its magnetic anisotropy energy by angle-dependent x-ray magnetic circular dichroism at the Fe L2,3 edge. By this technique, one can deduce the magnetic dipole moment mT, which represents the anisotropic spatial distribution of spin-polarized electrons, and the orbital moment anisotropy (OMA) of Fe 3d electrons. Detected finite mT indicates that the spin-polarized Fe 3d electrons are distributed preferentially in the out-of-plane direction of the films. This mT of Fe overwhelms the positive contribution of OMA to PMA and reduces the PMA of L10-ordered FePt thin films, consistent with a previous first-principles calculation. The present result implies that a large positive contribution of the non-magnetic element Pt rather than Fe governs the PMA of L10-ordered FePt thin films.
Shibata et al. (Mon,) studied this question.