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From Fe 3 O 4 /NiO bilayers to NiFe 2 O 4 -like thin films through Ni interdiffusion

DOI: 10.1103/PhysRevB.94.094423 DOI Help

Authors: Olga Kuschel (Osnabrück University) , R. Buß (Osnabrück University) , W. Spiess (Osnabrück University) , T. Schemme (Osnabrück University) , J. Wöllermann (Osnabrück University) , K. Balinski (Osnabrück University) , A. T. N'diaye (2Advanced Light Source, Lawrence Berkeley National Laboratory) , T. Kuschel (University of Bielefeld) , J. Wollschläger (Osnabrück University) , K. Kuepper (Osnabrück University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 94 , PAGES 094423

State: Published (Approved)
Published: September 2016
Diamond Proposal Number(s): 10511

Abstract: 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 Ni2+ ions out of NiO into Fe3O4 ultrathin films, resulting in off-stoichiometric nickel ferrite–like thin layers. We synthesized epitaxial Fe3O4/NiO bilayers on Nb-doped SrTiO3(001) substrates by means of reactive molecular beam epitaxy. Subsequently, we performed an annealing cycle comprising three steps at temperatures of 400 ◦C, 600 ◦C, and 800 ◦C 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 NiFe2O4. 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 Ni2+ and Fe3+ ions and the Fe3+ 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.

Journal Keywords: HAXPES, ferrites, interdiffusion

Subject Areas: Physics, Materials

Instruments: I09-Surface and Interface Structural Analysis

Other Facilities: DESY PETRA III P08

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