Microstructure of NiFe Epitaxial Thin Films Grown on MgO Single-Crystal Substrates

NiFe epitaxial thin films were prepared on MgO(100) and MgO(110) single-crystal substrates heated at 300° C by ultra-high vacuum molecular beam epitaxy. In the early stage of film growth on MgO(100) substrate, formation of NiFe (112¿0) epitaxial thin film with hcp structure is observed by in-situ RHEED. With increasing the film thickness, fcc-NiFe(100) phase appears and the RHEED intensity from fcc-NiFe(100) crystal increases. X-ray diffraction and high-resolution transmission electron microscopy indicate that the resulting film structure is fcc-NiFe(100), suggesting that the metastable hcp-NiFe (112¿0) phase is observable only during film growth process. On the contrary, NiFe(110) _fcc single-crystal film grows epitaxially on MgO(110) substrate. Atomically sharp boundaries are recognized between NiFe thin films and MgO substrates, where misfit dislocations are periodically introduced in the films at the NiFe/MgO interfaces reducing the lattice mismatches. Out-of-plane and in-plane lattice spacings of these films agree with the values of bulk NiFe crystal with very small errors of less than 0.5%, suggesting that the strains in the NiFe films are very small.