Effects of density of states on bias dependence in magnetic tunnel junctions

We present a study of the bias dependence of resistance and magnetoresistance (MR) in magnetic tunnel junctions both experimentally and theoretically. A modified Brinkman model has been proposed by incorporating the voltage-dependent density of states of the ferromagnetic electrodes to explain the bias dependence of magnetoresistance and resistance in a large bias range. It has been found that a reasonable variation of the effective density of states is necessary to fit the rapid decrease of resistance and magnetoresistance under large voltage bias, indicating that the most significant contribution of the bias dependence of tunneling MR comes from the electronic structure of ferromagnetic electrodes. The calculated polarizations based on these extrapolated densities of states are in good agreement with reported values by various experiments.