INVESTIGATIONS OF THE INTERPLAY BETWEEN CRYSTALLINE AND MAGNETIC-ORDERING IN FE3O4 NIO SUPERLATTICES/

Using SQUID magnetometry and both x-ray- and neutron-diffraction techn iques, we have studied the structural and magnetic ordering of a serie s of Fe3O4/NiO superlattices grown by MBE. X-ray diffraction reveals t hat the superlattices are coherent, single phase crystals with narrow interfaces. Symmetry differences between the Fe3O4 spinel and NiO rock salt structures lead to interfacial stacking faults, manifested in som e diffraction intensities. Analysis of the neutron-diffraction spectra show that the NiO antiferromagnetic ordering is coherent through seve ral superlattice bilayers, while the Fe3O4 magnetic ordering is confin ed to individual interlayers by stacking faults in all superlattices b ut those with thinnest (less than or equal to 10 Angstrom) NiO interla yers. Neutron diffraction and SQUID magnetometry have been used to stu dy the Fe3O4 Venvey phase transition in thin-layered superlattices. Th e charge ordering in superlattices such as [Fe3O4 (75 Angstrom)\NiO (9 Angstrom)](500), below the Venvey transition, directly observable in (4, 0, 1/2) neutron intensities, indicates a shift to higher temperatu re of the charge ordering transition from the bulk Fe3O4 T-Verwey at 1 23 K. We also describe ongoing efforts to extract the moment distribut ion in these superlattices from field dependent high-angle neutron dif fraction.