Abstrakt
Exchange interaction through interface between a ferromagnet and an antiferromagnet may result in the magnetic exchange bias (EB) effect [1]. The EB manifests itself as a shift of a magnetic hysteresis loop along the field direction.
This property has become of a great technological value for applications in magnetic sensors based on spin-valves or tunnel junctions [2]. In this work, we studied crystal structure and magnetic EB effect in bilayers of antiferromagnetic UO2 (bulk Néel temperature 30.8 K) with ferrimagnetic Fe3O4.
A reference UO2/Fe sample has been also prepared and studied. We used reactive sputter deposition from metallic U and Fe targets to prepare a set of samples with different Fe3O4 thicknesses while the thickness of the UO2 layer was kept constant.
The samples were grown on commercially available CaF2 (100) and (111) substrates (CaF2 has an identical crystal structure and a lattice parameter within 0.5% of UO2). The layer of UO2 was deposited onto the substrate at elevated temperature (850 K), using a partial oxygen pressure of 1.2x10-6 mbar (Ar pressure of 6x10-3 mbar).
Fe3O4 was deposited on the top of UO2 at the same partial oxygen pressure but at room temperature, in order to avoid interdiffusion. The stoichiometry of each deposited layer was controlled by X-ray Photoelectron Spectroscopy (XPS).
A magnesium cap was deposited for protection on top of each sample. The samples have been characterized using X-ray diffraction