Structural origin of magnetic anisotropy in Co-Pt alloy films probed by polarized XAFS

Polarized X-ray absorption fine structure (XAFS) measurements at the Co K and Pt L-3 edges show that the perpendicular magnetic anisotropy found in epitaxial fee CoPt3 (111) films stems from the existence of anisotropic local ordering. Such ordering, induced during the codeposition process and dependent on the growth temperature, is characterized by preferential CoCo pairs in time film plane, balanced by preferential CoPt pairs out of the planet resulting from some Co 2D-segregation. Polarized XAFS at the Pt edge reveals similar anisotropic local ordering in epitaxial hcp Co3Pt (0001) films exhihiting a larger magnetocrystalline anisotropy compared to that of bulk hcp Co. Besides, a polarization dependence of the Co XANES profile is observed only for the Co3Pt films exhibiting hcp symmetry.