Inversion of spin polarization and tunneling magnetoresistance in spin-dependent tunneling junctions

An inversion of spin polarization has been observed in spin-dependent tunne ling (SDT) junctions with Ta2O5 and Ta2O5/Al2O3 barriers. The resistance of an SDT junction is found to be lower with magnetization of the ferromagnet ic electrodes aligned antiparallel under specific voltage configurations. T he tunneling magnetoresistance effect changes sign with applied voltage and varies from +1% to -4% at room temperature. This inversion is believed to be due to the change in sign with bias of the spin polarization of one of t he two electrodes. The strong dependence on voltage suggests negative spin polarization could arise from the densities of states for spins being diffe rent at the two electrode/barrier interfaces. [S0031-9007(98)08200-3].