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

We report spin-dependent perpendicular transport in the magnetic trilayer junction structure ${\mathrm{La}}_{\text{0.67}}$ Sr${}_{\text{0.33}}$ MnO${}_3$ /SrTiO${}_3$ /La${}_{\text{0.67}}$ Sr${}_{\text{0.33}}$ MnO${}_3.$ Large (factor of 5) changes of magnetoresistance induced by a field of $\text{∼200}$ Oe are observed at $\text{4.2}$ K. Junction $\mathrm{I–V}$ characteristics at low temperatures are consistent with a metal–insulator–metal tunneling process with a large spin-polarization factor of $\text{0.81}$ 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 SrTiO${}_3$ barrier and therefore is not an intrinsic limit to the magnetoresistance performance of the device at high temperatures.