Effect of thermal-annealing on the magnetoresistance of manganite-based junctions

Thermal-annealing has been widely used in modulating the oxygencontent of manganites. In this work, we have studied the effect ofannealing on the transport properties and magnetoresistance ofjunctions composed of a La_0.9Ca_0.1MnO_{3 + delta} filmand a Nb-doped SrTiO₃ substrate. We have demonstrated that themagnetoresistance of junctions is strongly dependent on theannealing conditions: From the junction annealed-in-air to thejunction annealed-in-vacuum, the magnetoresistance near 0-V bias canvary from sim --60% to sim 0. A possible mechanismaccounting for this phenomenon is discussed.