Observation of inverse magnetoresistance in perovskite oxide tunnel junctions

We have observed a distinct inverse magnetoresistance in a hybrid tunnel junction. Two types of perovskite oxides, La 0.67 Sr 0.33 MnO 3 and SrRuO 3 , were used as ferromagnetic electrodes with an SrTiO 3 barrier in between them. Micron‐scale junctions were fabricated from 90° off‐axis sputtered trilayers, using standard optical lithography. Homo‐junctions that incorporate either La 0.67 Sr 0.33 MnO 3 or SrRuO 3 as both electrodes showed only normal positive magnetoresistances. In contrast, a clear inverse magnetic switching was found at 10 K for the hybrid junction. The spin polarization of SrRuO 3 is about –9% as calculated based upon Julliere model, which is in quantitative agreement with the value (–10%) determined by the earlier tunneling experiment on SrRuO 3 /SrTiO 3 /Al structures. This is not only the manifestation of the existence of a negatively polarized material at the Fermi level, but also demonstrates that the widely‐cited Julliere model is applicable even to a negative polarization case. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)