Nanoconstriction microscopy of the giant magnetoresistance in cobalt/copper spin valves

We use nanometer-sized point contacts to a Co/Cu spin valve to study the gi ant magnetoresistance (GMR) of only a few Co domains. The measured data sho w strong device-to-device differences of the GMR curve, which we attribute to the absence of averaging over many domains. The GMR ratio decreases with increasing bias current. For one particular device, this is accompanied by the development of two distinct GMR plateaus, the plateau level depending on bias polarity and sweep direction of the magnetic field. We attribute th e observed behavior to current-induced changes of the magnetization, involv ing spin transfer due to incoherent emission of magnons and self-field effe cts. (C) 1999 American Institute of Physics. [S0003-6951(99)01049-9].