Investigation of perpendicular magnetic anisotropy in Pd/Co2FeSi/MgO structures with evaluations of magnetic property, crystal structure, and elemental mapping

The authors investigated origins of perpendicular magnetic anisotropy (PMA) in a multilayer of full-Heusler Co2FeSi (CFS) alloys, MgO, and Pd. The CFS thickness dependence of the magnetic properties indicated that the bulk magnetic anisotropy of the CFS layers also contributed to the PMA even in the samples where the CFS thickness tCFS was 10 nm. The anisotropy constant was drastically increased at tCFS = 1.8 nm, and 0.7 nm. The crystal structure analysis indicated that CFS layers had the tensile strain for out-of-plane when the thickness was thicker than 1.8 nm, which can induce the bulk magnetic anisotropy via the magnetostrictive effect. The elemental mapping by a scanning transmission electron microscope revealed that approximately 2 nm thick Pd existed at the CFS/MgO interface. The authors considered the whole CFS layers could contain Pd when the thickness of CFS was less than 2 nm. This Pd might cause the bulk anisotropy of the samples with the CFS thickness below 2 nm since some Pd alloys and Pd/Co and Pd/Fe multilayers have large bulk magnetic anisotropy.