Investigations of the interplay between crystalline and magnetic ordering in Fe3O4/NiO superlattices

Abstract

Using SQUID magnetometry and both x-ray- and neutron-diffraction techniques, we have studied the structural and magnetic ordering of a series of Fe3O4/NiO superlattices grown by MBE. X-ray diffraction reveals that the superlattices are coherent, single phase crystals with narrow interfaces. Symmetry differences between the Fe3O4 spinel and NiO rocksalt structures lead to interfacial stacking faults, manifested in some diffraction intensities. Analysis of the neutron-diffraction spectra show that the NiO antiferromagnetic ordering is coherent through several superlattice bilayers, while the Fe3O4 magnetic ordering is confined to individual interlayers by stacking faults in all superlattices but those with thinnest (≤10 Å) NiO interlayers. Neutron diffraction and SQUID magnetometry have been used to study the Fe3O4 Verwey phase transition in thin-layered superlattices. The charge ordering in superlattices such as [Fe3O4 (75 Å)‖NiO (9 Å)]500, below the Verwey transition, directly observable in (4, 0, 1/2) neutron intensities, indicates a shift to higher temperature of the charge ordering transition from the bulk Fe3O4 TVerwey at 123 K. We also describe ongoing efforts to extract the moment distribution in these superlattices from field dependent high-angle neutron diffraction.