Impact of Strain and Morphology on Magnetic Properties of Fe₃O₄/NiO Bilayers Grown on Nb:SrTiO₃(001) and MgO(001)

Autor(en): Kuschel, Olga 
Pathé, Nico 
Schemme, Tobias 
Ruwisch, Kevin
Rodewald, Jari 
Buss, Ralph 
Bertram, Florian 
Kuschel, Timo 
Kuepper, Karsten 
Wollschläger, Joachim 
Affiliationen: Department of Physics and Center of Physics and Chemistry of New Materials, Osnabrück University, 49076 Osnabrück, Germany. oschuckm@uos.de. Department of Physics and Center of Physics and Chemistry of New Materials, Osnabrück University, 49076 Osnabrück, Germany. npathe@uos.de. Department of Physics and Center of Physics and Chemistry of New Materials, Osnabrück University, 49076 Osnabrück, Germany. toschemm@uos.de. Department of Physics and Center of Physics and Chemistry of New Materials, Osnabrück University, 49076 Osnabrück, Germany. kruwisch@uos.de. Department of Physics and Center of Physics and Chemistry of New Materials, Osnabrück University, 49076 Osnabrück, Germany. jarodewa@uos.de. Department of Physics and Center of Physics and Chemistry of New Materials, Osnabrück University, 49076 Osnabrück, Germany. rbuss@uos.de. Deutsches Elektronen-Synchrotron (DESY), Photon Science, 22607 Hamburg, Germany. florian.bertram@desy.de. Center for Spinelectronic Materials and Devices, Department of Physics, Bielefeld University, 33615 Bielefeld, Germany. tkuschel@physik.uni-bielefeld.de. Department of Physics and Center of Physics and Chemistry of New Materials, Osnabrück University, 49076 Osnabrück, Germany. kkuepper@uos.de. Department of Physics and Center of Physics and Chemistry of New Materials, Osnabrück University, 49076 Osnabrück, Germany. jwollsch@uos.de.
Erscheinungsdatum: 2018
Journal: Materials / MDPI
Volumen: 11
Ausgabe: 7
Zusammenfassung: 
We present a comparative study of the morphology and structural as well as magnetic properties of crystalline Fe₃O₄/NiO bilayers grown on both MgO(001) and SrTiO₃(001) substrates by reactive molecular beam epitaxy. These structures were investigated by means of X-ray photoelectron spectroscopy, low-energy electron diffraction, X-ray reflectivity and diffraction, as well as vibrating sample magnetometry. While the lattice mismatch of NiO grown on MgO(001) was only 0.8%, it was exposed to a lateral lattice mismatch of −6.9% if grown on SrTiO₃. In the case of Fe₃O₄, the misfit strain on MgO(001) and SrTiO₃(001) amounted to 0.3% and −7.5%, respectively. To clarify the relaxation process of the bilayer system, the film thicknesses of the magnetite and nickel oxide films were varied between 5 and 20 nm. While NiO films were well ordered on both substrates, Fe₃O₄ films grown on NiO/SrTiO₃ exhibited a higher surface roughness as well as lower structural ordering compared to films grown on NiO/MgO. Further, NiO films grew pseudomorphic in the investigated thickness range on MgO substrates without any indication of relaxation, whereas on SrTiO₃ the NiO films showed strong strain relaxation. Fe₃O₄ films also exhibited strong relaxation, even for films of 5 nm thickness on both NiO/MgO and NiO/SrTiO₃. The magnetite layers on both substrates showed a fourfold magnetic in-plane anisotropy with magnetic easy axes pointing in 100 directions. The coercive field was strongly enhanced for magnetite grown on NiO/SrTiO₃ due to the higher density of structural defects, compared to magnetite grown on NiO/MgO.
DOI: 10.3390/ma11071122
Externe URL: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6073869

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