1 research outputs found
From Fe3O4/NiO bilayers to NiFe2O4-like thin films through Ni interdiffusion
Ferrites with (inverse) spinel structure display a large variety of electronic and magnetic properties, making some of them interesting for potential applications in spintronics. We investigate the thermally induced interdiffusion of Ni ions out of NiO into FeO ultrathin films, resulting in off-stoichiometric nickel ferrite–like thin layers. We synthesized epitaxial FeO bilayers on Nb-doped SrTiO(001) substrates by means of reactive molecular beam epitaxy. Subsequently, we performed an annealing cycle comprising three steps at temperatures of 400C, 600C, and 800C under an oxygen background atmosphere. We studied the changes of the chemical and electronic properties as result of each annealing step with help of hard x-ray photoelectron spectroscopy and found a rather homogeneous distribution of Ni and Fe cations throughout the entire film after the overall annealing cycle. For one sample we observed a cationic distribution close to that of the spinel ferrite NiFeO. Further evidence comes from low-energy electron diffraction patterns indicating a spinel-type structure at the surface after annealing. Site- and element-specific hysteresis loops performed by x-ray magnetic circular dichroism uncovered the antiferrimagnetic alignment between the octahedral coordinated Ni and Fe ions and the Fe ion in tetrahedral coordination. We find a quite low coercive field of 0.02 T, indicating a rather low defect concentration within the thin ferrite films