Structural study of nanometer-sized iron crystallites in single crystalline iron-MgO composite films.

Single crystalline composite films of iron and MgO are prepared by a simultaneous vacuum deposition technique. The structures of the composite films, especially of the iron crystallites embedded, are studied by high-resolution electron microscopy and nanometer-area electron diffraction. The alpha-iron (b.c.c.) crystallites of 1 nm in size are epitaxially embedded in single crystalline MgO films, the orientation being (011)[100]Fe parallel (001)[100]MgO and (001)[110]Fe parallel (001)[100]MgO. A heat treatment of the as-grown films at 500-1,000 degrees C brings about a phase transformation of the crystallites from alpha-iron to gamma-iron (f.c.c.), followed by a grain growth of alpha-iron and finally the growth of the spinel, MgFe2O4. The gamma-iron crystallites transformed are circular plates and have strains at the periphery to accommodate the surrounding MgO-matrix. The magnetic property of the composite films is also reported.