Inverse tunnel magnetoresistance in Co/SrTiO3/La0.7Sr0.3MnO3: New ideas onspin-polarized tunneling

We report tunnel magnetoresistance (TMR) measurements on Co/SrTiO3/Lao(0.7) Sr(0.3) MnO3 junctions. The half-metallic Lao(0.7)Sr(0.3)MnO(3) electrode i s used as a spin analyzer. The large (-50%) inverse TMR indicates a negativ e spin polarization of Co, in agreement with the density of states (DOS) of the d band in Co. The bias dependence of the TMR, with a maximum inverse T MR at -0.4 V and a crossover to normal TMR above +0.8 V, reflects the struc ture of this DOS. Our results demonstrate that the choice of the insulating barrier can strongly influence and even reverse the spin polarization of t unneling electrons, [S0031-9007(99)09225-X].