The Cr local structure in epitaxial CrPt3(111) films probed by polarized XAFS

The local atomic structure of CrPt3(111) thin films grown by molecular beam epitaxy at different temperatures (400 and 850 °C) has been investigated by polarized x-ray absorption spectroscopy (XAS) at the chromium K edge. Previous x-ray diffraction and magnetic studies have revealed that films grown at 850 °C present the L12 chemically long range ordered structure and are ferrimagnetic with the occurrence of perpendicular magnetic anisotropy (PMA). In contrast, films grown at 400 °C, which are non-magnetic, do not show any indication of L12-type long range order. From the polarization dependence of XAS, different chemical orders in the film plane and perpendicular to it are reported for the non-magnetic film: Cr absorbers are surrounded by only Pt atoms in the film plane while out of the film plane Cr nearest neighbours are observed. The higher deposition temperature of the ferrimagnetic film (850 °C) leads to a more isotropic structure reducing the Cr–Cr out-of-plane correlations, as expected from the L12 ordered structure. These findings show that ferrimagnetism in CrPt3 films is strongly sensitive to the Cr–Cr correlations. Furthermore, the remaining in-plane tensile deformation found in the ferrimagnetic film is too small for yielding the observed PMA. It is suggested that the strong PMA originates from the ferromagnetic coupling between Cr second-nearest neighbours lined up along the \langle 001\rangle directions and which develop an orbital moment parallel to the spin moment as found by relativistic energy band calculations.