Interfacial effects on the tunneling magnetoresistance in L a0.7 S r0.3Mn O3/MgO/Fe tunneling junctions

Abstract

We report on magnetotransport properties on La0.7Sr0.3MnO3/MgO/Fe tunnel junctions grown epitaxially on top of (001)-oriented SrTiO3 substrates by sputtering. It is shown that the magnetoresistive response depends critically on the MgO/Fe interfacial properties. The appearance of an FeOX layer by the interface destroys the Δ1 symmetry filtering effect of the MgO/Fe system and only a small negative tunneling magnetoresistance (TMR) (∼-3%) is measured. However, in annealed samples a switchover from positive TMR (∼+25% at 70 K) to negative TMR (∼-1%) is observed around 120 K. This change is associated with the transition from semiconducting at high T to insulating at low T taking place at the Verwey transition (TV∼120K) in Fe3O4, thus suggesting the formation of a very thin slab of magnetite at the MgO/Fe interface during annealing treatments. These results highlight the relevance of interfacial properties on the tunneling conduction process and how it can be substantially modified through appropriate interface engineering.