Formation and magnetic properties of artificial superlattice of CoOFe 3O 4

Abstract

Superlattices composed of ultrathin layers of CoO and Fe 3O 4 were prepared by alternate deposition onto rock salt using reactive evaporation. The structure was investigated by electron diffraction and X-ray diffraction. The X-ray patterns with satellite peaks are in good agreement with calculations based on a one-dimensional model in which the lattice spacings perpendicular to the interface are assumed to have the bulk values. The 57Fe Mössbauer spectra at room temperature show the features of bulk Fe 3O 4. The superlattices showed an asymmetric magnetic hysteresis at 77 K and room temperature induced by magnetic cooling. The deformation and shift of the hysteresis loop from the origin was more remarkable with decreasing layer thickness. The hysteresis loop of the sample [ CoO(2.2 nm) Fe 3 O 4(9.0 nm) ] × 10 is asymmetric even at room temperature. For this sample a maximum occurs in the magnetization-temperature curve at 338 K on heating from 77 K and this shows that an interlayer exchange interaction between these antiferromagnetic and ferrimagnetic layers exists at least up to the temperature corresponding to the maximum. The saturation magnetization of Fe 3O 4 decreases abruptly with decreasing thickness of the Fe 3O 4 layer.