Reduced magnetoresistance in magnetic tunnel junctions caused by geometrical artifacts

Spuriously reduced magnetoresistance (MR) ratios have been observed in magn etic tunnel junctions in which a square contact portion with dimensions sma ller than the width of the lead electrodes connects both the top and bottom lead electrodes. The phenomenon becomes apparent by measuring the magnetor esistance of the junctions with various sizes systematically varied under a fixed line width of the electrodes. Observed junction size dependence of r esistance (R)xarea(A) products and MR ratios were analyzed through finite d ifference calculation, and it was found that there exist junction sizes for which RxA products and MR ratios are larger and smaller, respectively, tha n the intrinsic ones. (C) 2000 American Institute of Physics. [S0003-6951(0 0)02745-5].