Abstract
A comparative study of the structure and magnetism of Fe/CoO(111) and Fe/CoO(001) epitaxial bilayers was performed to investigate the role of uncompensated spins in the exchange bias (EB) phenomenon. Low-energy electron diffraction, x-ray photoelectron spectroscopy, conversion electron Mössbauer spectroscopy (CEMS), and the magneto-optic Kerr effect were used to characterize the structural and magnetic properties of the bilayers. Magnetically compensated and uncompensated CoO films were prepared using molecular beam epitaxy through the evaporation of single Co atomic layers and their subsequent oxidation (layer-by-layer technique) on MgO crystals with (001) and (111) orientations. Two-monolayer-thick Fe probes located on top of the oxide films and covered with Fe allowed for an analysis of the interfacial chemical and magnetic structure using CEMS. For both structures, submonolayer oxidation of the iron detected at the Fe/CoO interface was found to be accompanied by the formation of a mixed FeCo region. The Fe layers showed fourfold magnetocrystalline anisotropy when grown on CoO(001) and weak uniaxial anisotropy when grown on CoO(111). Although the structural quality and composition of the two structures were comparable, they exhibited distinct EB properties. A hysteresis loop shift as high as 354 Oe at 80 K was obtained for the Fe/CoO(111) bilayer, compared to only 37 Oe for the magnetically compensated Fe/CoO(001).
4 More- Received 17 June 2013
DOI:https://doi.org/10.1103/PhysRevB.88.085442
©2013 American Physical Society