INTERFACE STRUCTURES OF GAMMA-IRON CRYSTALLITES EMBEDDED IN MAGNESIUM-OXIDE CRYSTALLINE FILMS

Nanometer-size gamma-iron (f.c.c.-iron) crystallites were prepared in Fe MgO composite films made by a vacuum-codeposition of Fe and MgO onto NaCl surfaces at 350-degrees-C. The crystallites were stable at room temperatures. High-resolution electron microscopy revealed that the crystallites were epitaxially embedded inside MgO single crystal films and the interfacial lattice was deformed for accommodation of lattice misfit of 14% between gamma-Fe and MgO. The magnetic property of the crystallites was measured to be ferromagnetic similar to usual alpha-Fe. The appearance of the ferromagnetism may originate partly from an expansion of the lattice constant of interface regions from 0.36 nm, which was calculated recently to be a saddle point of the magnetic phase-transition from anti-ferromagnetism to ferromagnetism. The interface structures were thus studied by high-resolution electron microscopy, nanometer-area electron diffraction and dark-field method.