Structure characterization of Pd/Co/Pd tri-layer films epitaxially grown on MgO single-crystal substrates

Pd/Co/Pd tri-layer films were prepared on MgO substrates of (001), (111), and (011) orientations at room temperature by ultra high vacuum rf magnetron sputtering. The detailed film structures around the Co/Pd and the Pd/Co interfaces are investigated by reflection high energy electron diffraction. Pd layers of (001)fcc, (111)fcc, and (011)fcc orientations epitaxially grow on the respective MgO substrates. Strained fcc-Co(001) single-crystal layers are formed on the Pd(001)fcc layers by accommodating the fairly large lattice mismatch between the Co and the Pd layers. On the Co layers,, Pd polycrystalline layers are formed. When Co films are formed on the Pd(111)fcc and the Pd(011)fcc layers, atomic mixing is observed around the Co/Pd interfaces and fcc-CoPd alloy phases are coexisting with Co crystals. The Co crystals formed on the Pd(111)fcc layers consist of hcp(0001) + fcc(111) and Pd(111)fcc epitaxial layers are formed on the Co layers. Co crystals epitaxially grow on the Pd(011)fcc layers with two variants, hcp(11̄00) and fcc(111). On the Co layers, Pd(011)fcc epitaxial layers are formed.