STRUCTURAL AND MAGNETIC-ORDERING IN IRON-OXIDE NICKEL-OXIDE MULTILAYERS BY X-RAY AND NEUTRON-DIFFRACTION

Presented are studies of the magnetic and structural ordering in superlattices composed of Fe3O4 and NiO, and their study by a variety of techniques including x-ray and neutron diffraction, and SQUID magnetometry. X-ray diffraction indicates that structures with individual layer thicknesses down to 8.5 angstrom grow as single crystals in registry with the substrate lattice with a layer-thickness-dependent tetragonal lattice distortion due to epitaxial and interfacial lattice mismatch. The lattice coherence of the Fe3O4 layers, however, is degraded by stacking faults between adjacent spinel layers. Neutron diffraction indicates that the NiO orders antiferromagnetically along the [111] direction with a magnetic coherence that extends over several superlattice bilayers, and the presence of an enhancement in the NiO Neel temperature in thin layered superlattices. These results are compared with SQUID magnetometry, which shows large anisotropy energies, but a lack of favored magnetization direction, indicating that the magnetic ordering in these systems is dominated by the exchange coupling across the interfaces.