Bias dependence of magnetic tunnel junctions

We report a source of bias dependence to the tunneling magnetoresistance of magnetic tunnel junctions. It arises when the non-Ohmic character of the tunneling process in a spatially extended junction causes the measured current-voltage characteristic to have a bias-voltage dependence different from that intrinsic to the junction. This leads to incorrect barrier height and thickness determinations, as well as to a large bias dependence of the differential tunneling magnetoresistance. This effect manifests itself when the electrode sheet resistance is comparable to or much larger than the zero-bias tunneling resistance. Magnetic tunnel junctions fabricated from colossal magnetoresistive magnetic oxides are typically in this resistance regime; metallic junctions with ultrathin electrodes may also show this effect.