Temperature dependent, non-ohmic magnetoresistance in doped perovskite manganate trilayer junctions

We report spin-dependent perpendicular transport in the magnetic trilayer junction structure La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3. Large (factor of 5) changes of magnetoresistance induced by a field- of similar to 200 Oe are observed at 4.2 K. Junction I-V characteristics at low temperatures are consistent with a metal-insulator-metal tunneling process with a large spin-polarization factor of 0.81 for the conduction electrons. Above 100 K, a variable range-hopping conduction shunts out the magnetoresistance contribution. This second conduction channel comes from the impurity states within SrTiO3 barrier and therefore is not an intrinsic limit to the magnetoresistance performance of the device at high temperatures. (C) 1997 American Institute of Physics.