Journal
APPLIED SURFACE SCIENCE
Volume 586, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.apsusc.2022.152672
Keywords
Cobalt ferrite; Ultrathin films; Mossbauer spectroscopy; In-situ characterization; Oxygen assisted molecular beam epitaxy; Pt(111)
Categories
Funding
- Spanish Ministry of Science and Innovation [RTI2018-095303-B-C51, RTI2018-095303-B-C53, MAT2017-86450-C4-1-R]
- Spanish Ministry of Science and Innovation through the Ramon y Cajal Contract [RYC-2017-23320, RTI2018-095303-C52]
- Regional Government of Madrid [S2018-NMT-4321]
- PROM Programme-International scholarship exchange of Ph.D. students and academics
- European Commission through the H2020 Project [720853]
- [RTI2018-095303-A-C52]
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CoFe2O4 thin films of different thicknesses were grown on Pt(111) and subsequently annealed. Annealing increased the grain size, induced magnetic ordering at room temperature, and caused cobalt segregation to the surface. Cationic distribution was affected by annealing in oxygen or vacuum.
CoFe2O4 thin films (5 nm and 20 nm thick) were grown by oxygen assisted molecular beam epitaxy on Pt(111) at 523 K and subsequently annealed at 773 K in vacuum or oxygen. They were characterized in-situ using Auger Electron Spectroscopy, Low-Energy Electron Diffraction, Scanning Tunneling Microscopy and Conversion Electron Mossbauer Spectroscopy. The as-grown films were composed of small, nanometric grains. Annealing of the films produced an increase in the grain size and gave rise to magnetic order at room temperature, although with a fraction of the films remaining in the paramagnetic state. Annealing also induced cobalt segregation to the surface of the thicker films. The measured Mossbauer spectra at low temperature were indicative of cobalt ferrite, the both films showing very similar hyperfine patterns. Annealing in oxygen or vacuum affected the cationic distribution, which was closer to that expected for an inverse spinel in the case of annealing in an oxygen atmosphere.
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