Exchange bias in UO2/Fe3O4 thin films above the Néel temperature of UO2

Magnetic exchange bias (EB) has been investigated on antiferromagnetic/ferrimagnetic heterostructures consisting of a stoichiometric UO2 film grown epitaxially on a LaAlO3 substrate and covered with highly textured Fe3O4 layers of variable thickness (t Fe3O4 = 90–700 Å). EB values reaching ∼2.6 kOe were observed at lowest temperatures in UO2/Fe3O4 with the thinnest Fe3O4. Magnetization measurements demonstrate that a remarkably large exchange bias in UO2/Fe3O4 is present at temperatures higher than the bulk N é el temperature of UO2 (T N = 30.8 K). Our study reveals a complex nature of the effect: we suggest that it is provided both by strong exchange coupling between UO2 and Fe3O4 and by exchange biasing within magnetite (up to 25% of the total effect at 5 K in the UO2/Fe3O4 sample with the largest EB). The former can be caused by proximity effects of Fe3O4 on T N combined with a magnetic anisotropy of UO2, persisting above a continuous magnetic-ordering transformation. For magnetite, the results indicate the presence of pinned moments up to 120 K that correlates with the change in the easy magnetization axis of Fe3O4 across the Verwey transition.

TERESHINA Evgenia;  BAO Zhaohui;  HAVELA L.;  DANIS S.;  KUEBEL Christian;  GOUDER Thomas;  CACIUFFO Roberto; 

2014-12-05

AMER INST PHYSICS

JRC90629

0003-6951,   

http://scitation.aip.org/content/aip/journal/apl/105/12/10.1063/1.4896635,    http://dx.doi.org/10.1063/1.4896635,    https://publications.jrc.ec.europa.eu/repository/handle/JRC90629,   

10.1063/1.4896635,