Voltage dependence of magnetoresistance in spin dependent tunneling junctions

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. (C) 1998 American Institute of Physics. [S0021-8979(98)28311-3].