NiO/Fe(001): Magnetic anisotropy, exchange bias, and interface structure

The magnetic and structural properties of NiO/Fe epitaxial bilayers grown on MgO(001) were studied using magnetooptic Kerr effect (MOKE) and conversion electron Mossbauer spectroscopy (CEMS). The bilayers were prepared under ultra high vacuum conditions using molecular beam epitaxy with oblique deposition. Two systems were compared: one showing the exchange bias (100ML-NiO/24ML-Fe), ML stands for a monolayer, and another where the exchange bias was not observed (50ML-NiO/50ML-Fe). For both, the magnetic anisotropy was found to be complex, yet dominated by the growth-induced uniaxial anisotropy. The training effect was observed for the 100ML-NiO/24ML-Fe system and quantitatively described using the spin glass model. The composition and magnetic state of the interfacial Fe layers were studied using Fe-57-CEMS. An iron oxide phase (Fe43+Fe12+O7), as thick as 31 angstrom, was identified at the NiO/Fe interface in the as-deposited samples. The ferrimagnetic nature of the interfacial iron oxide film explains the complex magnetic anisotropy observed in the samples. (C) 2013 AIP Publishing LLC.