Voltage dependence of magnetoresistance in spin dependent tunneling junctions

Abstract

The voltage dependence of magnetoresistance in spin dependent tunneling (SDT) junctions was studied experimentally and theoretically. Different magnetoresistance (MR)-V dependence in various patterned junctions was observed and correlated with other technologically important parameters, including the magnitude of the MR, linearity of the current–voltage characteristic, temperature dependence of the junction resistance, and the MR. A phenomenological model based on a spin-independent two-step tunneling via defect states in the barrier, in addition to the spin-dependent direct tunneling, is proposed to account for the MR-V dependence. The MR ratio is determined by the ratio of the two currents. The MR-V dependence results from a stronger voltage dependence of the two-step tunneling current compared to that of the direct tunneling current. The same model also satisfactorily predicts other properties of SDT junctions. A high quality barrier is required to minimize the MR-V dependence and improve other junction properties. The approach to achieving desirable junction impedance for data storage applications is discussed.