Incommensurate superlattice modulation surviving down to an atomic scale in sputter-deposited Co/Pt(111) epitaxial multilayered films

Abstract

We report the structural feature of sputter-deposited epitaxial [Co (0.2 nm)/Pt (0.2–1.0 nm)] multilayered films prepared with various periodic structural designs consisting of non-integer numbers of Co and Pt monoatomic layers on an atomically flat Ru(0001). Sharp superlattice modulation peaks and their systematic changes with the Pt thicknesses were observed in the x-ray diffraction (XRD) spectrum. The formation of periodic structures shows that layer-by-layer like growth occurs and the resulting incommensurate superlattice modulation survives down to an atomic scale even in the sputter-deposited Co/Pt multilayers. Magnetic properties were also investigated for the Co/Pt multilayers. Interestingly, the maximum perpendicular magnetic anisotropy Ku of 3 × 106 erg/cm3 was obtained for the [Co (0.2 nm)/Pt (0.3 nm)] multilayer exhibiting incommensurate superlattice modulation peaks, while the [Co (0.2 nm)/Pt (0.2 nm)] multilayer with a L11-like XRD peak showed a smaller Ku. A cross-sectional high-angle annular dark-field scanning transmission electron microscopy analysis revealed that a partially L11-ordered CoPt structure is formed in the [Co 0.2 nm/Pt 0.2 nm] multilayer, interpreting the observed Ku. This study gives a new insight into the structural feature of sputter-deposited Co/Pt multilayers useful for a wide range of spintronic devices, such as magnetic tunnel junctions.