Growth and characterization of TiO2 as a barrier for spin-polarized tunneling

We report on the elaboration and characterization of tunnel junctions based on La2/3Sr1/3MnO3 and TiO2. The structural analysis shows that TiO2 grows epitaxially in the anatase phase and forms flat interfaces with the adjacent layers. Resistance maps of a La2/3Sr1/3MnO3/TiO2 bilayer reveal a homogeneous resistance level. After patterning tunnel junctions, we obtain a large positive tunneling magnetoresistance (TMR) at low temperature for La2/3Sr1/3MnO3/TiO2/La2/3Sr1/3MnO3 junctions and a negative TMR in the case of La2/3Sr1/3MnO3/TiO2/Co. This negative TMR reflects a negative spin polarization of Co at the interface with TiO2, in analogy with recent experimental results for the Co/SrTiO3 interface.