Exchange bias in iron oxide nanoclusters

Iron oxide nanoclusters have been prepared by the gas-phase aggregation technique to form thin film structures with very high exchange bias values (up to 3000Oe at low temperatures). Composition has been analysed by x-ray absorption and Mössbauer spectroscopies in order to elucidate the actual origin of the observed magnetic behaviour. The formation of a metaloxide coreshell arrangement to explain the observed exchange bias has to be discarded since results show no metallic iron content and the main presence of α-Fe2O3. The observed weak ferromagnetism and exchange bias are in agreement with the obtained size of α-Fe 2O3 nanoparticles: weak ferromagnetism because of the well-known spin canting in this antiferromagnetic structure and exchange bias because of the interaction between different spin sublattice configurations promoted by the modification of iron coordination in α-Fe 2O3 nanoparticles. Moreover, the preparation method is proposed for tuning both magnetization and exchange bias values by modification of the preparation conditions of α-Fe2O3 nanoparticles, which open new possibilities in the design of new materials with required properties. © 2011 IOP Publishing Ltd.This work has been supported by the Spanish MICINN under contracts MAT2009-08786 and CSD2009-00013 and by the regional government of Madrid though contract S2009/MAT-1756. JSM and MAL-M are grateful to MICINN for the financial support within the JdlC program. We would like to thank the SpLine CRG beamline staff at ESRF for assistance during x-ray absorption experiments.Peer Reviewe