| AVS 62nd International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Wednesday Sessions |
| Session AC+AS+MI-WeM |
| Session: | Magnetism, Complexity and Superconductivity in the Actinides and Rare Earths |
| Presenter: | Evgeniya Tereshina, Institute of Physics ASCR, Czech Republic |
| Authors: | E. Tereshina, Institute of Physics ASCR, Czech Republic Z. Bao, PANalytical B.V., Netherlands L. Havela, Charles University in Prague, Czech Republic R. Springell, University of Bristol, UK S. Danis, Charles University in Prague, Czech Republic A. Mackova, Nuclear Physics Institute ASCR, Czech Republic T. Gouder, Institute for Transuranium Elements (ITU), Germany R. Caciuffo, Institute for Transuranium Elements (ITU), Germany |
| Correspondent: | Click to Email |
Interfacial exchange interaction in bilayers consisting of two dissimilarly ordered magnetic materials (e.g. an antiferromagnet (AF) and a ferro- or ferrimagnet (F)) may give rise to a phenomenon called the magnetic exchange bias (EB) effect [1]. The EB manifests itself as a shift of a magnetic hysteresis loop along the field direction when the bilayer is field-cooled below the Néel temperature (TN) of the AF. This property is of great value for magnetic recording applications. Despite the conceptual simplicity, a generally accepted theory that predicts the EB behavior for an apt pair of materials is still missing. The reason for that might be in poorly defined interface structure in both magnetic and crystallographic aspects.
Critical dependence of EB on magnetic anisotropy brings us the possibility to use actinides with strong spin-orbit interaction as the key ingredient. Here we report exchange bias studies in magnetic bilayers consisting of a stoichiometric UO2 film grown epitaxially on different substrates and covered with polycrystalline metallic (Ni80Fe20 and Fe) and highly textured oxide (Fe3O4) layers of variable thickness. Large longitudinal exchange bias ~2.6 kOe is found in UO2/Fe3O4 bilayers [3] while UO2 combined with metallic ferromagnets displays perpendicular exchange coupling with an order of magnitude smaller EB. Interestingly, unusual effects in UO2/Fe3O4 were observed, namely, exchange bias did not vanish at TN of UO2. Apart from the fact that single layers of magnetite were showing some EB (not more than 25 % of the total effect in UO2/Fe3O4), the EB in UO2/Fe3O4 bilayers exceeded notably that of the single Fe3O4's to approx. 70 K that was attributed to possible proximity effects of Fe3O4 on TN of UO2 and/or to the magnetic anisotropy of UO2 preserved locally above TN. The effects were observed for the samples of quality controlled by different methods such as X-ray Photoelectron Spectroscopy, conventional X-ray Diffraction, Transmission Electron Microscopy and Rutherford Backscattering Spectroscopy. The work has been supported by the Czech Science Foundation, grant No. 13-25866P.
[1] W. H. Meiklejohn and C. P. Bean, “New magnetic anisotropy”, Phys. Rev. B 102, 1413 (1956).
[2] V. Sechovsky, L. Havela, in: Magnetic Materials, K.H.J. Buschow (Ed.), Elsevier, Amsterdam, 1998, Vol. 11, p. 1.
[3] E. A. Tereshina et al., Appl. Phys. Lett. 105, 122405 (2014).