González Herrera, Elvira MaríaFolgueras, A. D.Escudero, R.Ferrer, J.M.Guinea, F.Vicent López, José Luis2023-06-202023-06-202007-02-211367-263010.1088/1367-2630/9/2/034https://hdl.handle.net/20.500.14352/52072© IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. We thank very useful discussions with J Moodera, M Eschrig and M Fogelstrom. This study was supported by MEC (FIS2005-0739, NAN2004-09087, MAT2005-23924E, MAT2002-0495-C02-01, BFM2003-03156), CAM (S-0505/ESP/0337) and Santander-UCM. Additionally, RE thanks Universidad Complutense and Ministerio de Educación y Ciencia for a sabbatical professorship. AD-F thanks Ministerio de Educación y Ciencia for a FPU grant (AP2002-1383).We have measured the tunnelling current in Nb/Nb_xO_y/Ni planar tunnel junctions at different temperatures. The junctions are in the intermediate transparency regime. We have extracted the current polarization of the metal/ferromagnet junction without applying a magnetic field. We have used a simple theoretical model, that provides consistent fitting parameters for the whole range of temperatures analysed. We have also been able to gain insight into the microscopic structure of the oxide barriers of our junctions.engAtribución 3.0 Españajournal articlehttp://dx.doi.org/10.1088/1367-2630/9/2/034http://iopscience.iop.orgopen access538.9SuperlatticesReflectionFísica de materialesFísica del estado sólido2211 Física del Estado Sólido