FERROMAGNETIC-RESONANCE AND SPIN ANISOTROPY IN IRON-OXIDE THIN-FILMS AND IRON-OXIDE NICKEL-OXIDE SUPERLATTICES

Oriented single-crystalline thin films of Fe3O4 and superlattices of Fe3O4/NiO have been grown using molecular-beam-epitaxy techniques on polished substrates of MgO(001). The 1-2-mum-thick superlattices have their Fe3O4 layer thicknesses held constant at 68 angstrom and the NiO thickness varied from 8.5 to 102 angstrom. We report the initial ferromagnetic resonance measurements made on these samples to investigate the effects that interfacial lattice distortion and interlayer coupling have on their magnetic ordering and anisotropy. These results are compared with structural and magnetic studies made on the same films using x-ray diffraction and magnetometry techniques. We find clear evidence in the trends of both the ferromagnetic resonance fields and the linewidths as a function of NiO thickness that coupling between the layers can change the in-plane anisotropy and the overall magnetic response. The single-layer Fe3O4-only sample behaves essentially like bulk magnetite.