Preparation and Characterization of Co/Pd Epitaxial Multilayer Films with Different Orientations

Co/Pd multilayer films were prepared on fcc-Pd underlayers of (001), (111), and (011) orientations hetero-epitaxially grown on MgO single-crystal substrates at room temperature by ultrahigh-vacuum rf magnetron sputtering. The structural and magnetic properties vary depending on the underlayer orientation. A multilayer film consisting of fct-Co(001) and fcc-Pd(001) single-crystal layers is formed on a Pd(001)_\text{fccunderlayer, whereas epitaxial multilayer films consisting of Co and Pd layers with fcc(111) and fcc(011) orientations are obtained on Pd(111)_\text{fccand Pd(011)_\text{fccunderlayers, respectively. For the film grown on the Pd(001)_\text{fccunderlayer, sharp interfaces are formed between the Co and Pd layers. On the other hand, atomic mixing is observed at the Co/Pd interface for the films grown on the Pd(111)_\text{fccand Pd(011)_\text{fccunderlayers. The CoPd-alloy layers are formed around these interfaces. The CoPd-alloy formation is enhanced in the order of $(001) < (111) < (011)$. The multilayer films grown on the Pd(111)_\text{fccand Pd(011)_\text{fccunderlayers show perpendicular magnetic anisotropies, whereas the film grown on the Pd(001)_\text{fccunderlayer is easily magnetized in in-plane directions. The magnetic properties are delicately affected by the crystallographic structures of Co/Pd multilayer films.