Transport and magnetoresistance effect in an oxygen-deficient SrTiO₃/La_0.67Sr_0.33MnO₃ heterojunction

An oxygen-deficient SrTiO₃/La_0.67Sr_0.33MnO₃ heterojunction is fabricated on an SrTiO₃ (001) substrate by a pulsed laser deposition method. The electrical characteristics of the heterojunction are studied systematically in a temperature range from 80 K to 300 K. The transport mechanism follows I ∝ exp (eV/nkT) under small forward bias, while it becomes space charge limited and follows I ∝ V^m(T) with 1.49< m <1.99 under high bias. Such a heterojunction also exhibits magnetoresistance (MR) effect. The absolute value of negative MR monotonically increases with temperature decreasing and reaches 26.7% at 80 K under H=0.7 T. Various factors, such as strain and oxygen deficiency play dominant roles in the characteristics.