The Cr local structure in epitaxialCrPt3(111) films probed using polarized x-ray absorption fine structure

Abstract

The local atomic structure of CrPt3(111) thin films grown by molecular beam epitaxy at different temperatures (400 and850 °C) has been investigated by polarized x-ray absorption spectroscopy (XAS) at the chromiumK edge. Previous x-ray diffraction and magnetic studies have revealed that films grown at850 °C presentthe L12 chemically long range ordered structure and are ferrimagnetic with the occurrenceof perpendicular magnetic anisotropy (PMA). In contrast, films grown at400 °C, which are non-magnetic, do not show any indication ofL12-type long range order. From the polarization dependence of XAS, different chemical orders inthe film plane and perpendicular to it are reported for the non-magnetic film: Cr absorbersare surrounded by only Pt atoms in the film plane while out of the film plane Cr nearestneighbours 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 fromthe L12 ordered structure. These findings show that ferrimagnetism inCrPt3 films is strongly sensitive to the Cr–Cr correlations. Furthermore, the remaining in-planetensile deformation found in the ferrimagnetic film is too small for yielding the observedPMA. It is suggested that the strong PMA originates from the ferromagnetic couplingbetween Cr second-nearest neighbours lined up along the directions and which develop an orbital moment parallel to the spin moment as found byrelativistic energy band calculations.