Structure and Magnetic Properties of Artificial Superlattice and Multilayered Films of Magnetic Oxides

The structure and magnetic properties of multilayered films composed of ultra-thin oxide layers are described. Superlattices of CoO/NiO and CoO/Fe3O4 were prepared by alternating deposition of each on rock salt or sapphire by reactive evaporation. Superlattices of CoO/Fe3O4 showed an asymmetric magnetic hysteresis at 77 K and at room temperature, induced by magnetic cooling. The Néel temperature of CoO in the superlattices was higher than the bulk value of 18° C. Multilayered films composed of SiO and magnetic oxides were reduced to metal or Fe3O4 using hydrogen gas. The reduced films maintained a periodicity similar to that of the original films. Co metal was present in the reduced films in the form of disperse ultrafine particles. Ultrathin Fe3O4 layers in reduced films exhibited antiferromagnetism, which was attributed to an unusual iron ion distribution, Fe³⁺1.4[Fe²⁺1.0Fe³⁺0.6]O4.