Interface correlated exchange bias effect in epitaxial Fe3O4 thin films grown on SrTiO3 substrates

Abstract

We report exchange bias effect in Fe3O4 films epitaxially grown on SrTiO3 substrates. This effect is related to the formation of Ti3+-vacancy complexes at the surface of SrTiO3 in ultrahigh vacuum that in turn triggers the growth of a thin antiferromagnetic (AFM) FeO layer (∼5 nm) at the interface. The picture of antiferromagnetic FeO interacting with native ferrimagnetic Fe3O4 matrix reasonably accounts for this anomalous magnetic behavior. With increasing film thickness from 17 to 43 nm, the exchange bias effect and the magnetization anomaly associated with the AFM phase transition of the FeO layer are progressively weakened due to the increase in the volume fraction of the Fe3O4 phase, indicating the interfacial nature of the exchange coupling. Our results highlight the important role of interface engineering in controlling the magnetic properties of iron oxide thin films.