We present a study of the bias dependence of resistance and magnetoresistance ͑MR͒ 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.

We have fabricated magnetic tunneling junctions by oxidizing a wedge-shaped aluminum layer to produce junctions with ideal oxidized as well as under and over oxidized junctions on a single wafer. By investigating the capacitance spectra, we are able to study the effects due to interface charge accumulation. The electron–electron interaction among accumulated interface charges leads to a voltage drop inside the magnetic electrodes, resulting in the measured capacitance differing from the geometric capacitance. We have extracted an interfacial capacitance of 16 μF/cm2 per interface and a screening length of 0.55 Å for FeNi electrodes.

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We present a study on the positions of conductance minima for the parallel and antiparallel magnetization configurations in magnetic tunnel junctions, both experimentally and theoretically. It is found that the conductance minima can have as much as a 100-mV shift from zero bias, and the shifts are spin dependent. These behaviors have not been observed in tunnel junctions based on nonmagnetic electrodes. By considering the voltage dependent density of states of ferromagnetic electrodes in the Brinkman model, the difference can be well explained. The results demonstrate that the density of states of the ferromagnetic electrodes play an important role in defining the bias dependence behaviors in magnetic tunnel junctions.