Observation of spin-dependent transport and large magnetoresistance in La_0.7Sr_0.3MnO₃/SrTiO₃/La _0.7Sr_0.3MnO₃ ramp-edge junctions

We have fabricated ferromagnet-insulator-ferromagnet junctions using a ramp-edge geometry based on (La_0.7Sr_0.3)MnO₃ ferromagnetic electrodes and a SrTiO₃ insulator. Pulsed laser deposition was used to deposit the multilayer thin films and the devices were patterned using photolithography and ion milling. As expected from the spin-dependent tunneling, the junction magnetoresistance is dependent on the relative orientation of the magnetization in the electrodes. A junction magnetoresistance (JMR) as large as 30% is observed at low temperatures and low fields. In addition, we have found that JMR is reduced at high temperatures (T> 100 K) and decreases monotonically with increasing field at high fields (0.5 T<H< 1 T). Possible causes for these are also discussed.