Low noise all-oxide magnetic tunnel junctions based on a La_0.7Sr_0.3MnO₃/Nb:SrTiO₃ interface

All-oxide magnetic tunnel junctions with a semiconducting barrier, formed by the half-metallic ferromagnet La_0.7Sr_0.3MnO₃ and n-type semiconductor SrTi_0.8Nb_0.2O₃, were designed, fabricated, and investigated in terms of their magneto-transport properties as a function of applied bias and temperature. We found that the use of the heavily Nb-doped SrTiO₃ as a barrier results in significant improvement in the reproducibility of results, i.e., of large tunnel magnetoresistance (TMR) ratios, and a spectral noise density reduced by three orders of magnitude at low temperature. We attribute this finding to a considerably decreased amount of point defects in SrTi_0.8Nb_0.2O₃, especially oxygen vacancies, compared with the conventional insulating SrTiO₃ barrier.