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/Fe 3 O 4 were prepared by alternating deposition of each on rock salt or sapphire by reactive evaporation. Superlattices of CoO/Fe 3 O 4 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 Fe 3 O 4 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 Fe 3 O 4 layers in reduced films exhibited antiferromagnetism, which was attributed to an unusual iron ion distribution, Fe ³⁺ 1.4 [Fe ²⁺ 1.0 Fe ³⁺ 0.6 ]O 4 .