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 super lattices composed of Fe3O4 and NiO, and their study by a variety of te chniques including x-ray and neutron diffraction, and SQUID magnetomet ry. X-ray diffraction indicates that structures with individual layer thicknesses down to 8.5 angstrom grow as single crystals in registry w ith 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 sta cking faults between adjacent spinel layers. Neutron diffraction indic ates that the NiO orders antiferromagnetically along the [111] directi on with a magnetic coherence that extends over several superlattice bi layers, 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 fav ored magnetization direction, indicating that the magnetic ordering in these systems is dominated by the exchange coupling across the interf aces.