Current distribution effects in magnetoresistive tunnel junctions

The influence of an inhomogeneous current density on the (magneto)resistance of a ferromagnet-insulator-ferromagnet tunnel junction in the cross-strip geometry is analyzed using a finite element approach. The four-probe resistance is smaller than the actual resistance for electrode resistances (in the junction area) comparable to or higher than the junction resistance. Even negative four-probe resistances can be obtained. The apparent resistance change due to the junction magnetoresistive effect also decreases, but always remains positive. This results in unrealistically large apparent magnetoresistance ratios which can even approach infinity, which explains some recent experiments. (C) 1997 American Institute of Physics. [S0003-6951(97)03245-2].