FLUCTUATION-DISSIPATION RELATION FOR GIANT MAGNETORESISTIVE 1 F NOISE/

We find that Co/Cu multilayers exhibiting giant magnetoresistance (GMR ) also show giant magneto resistive 1/f noise. The largest component o f this noise (which peaks at magnetic fields maximizing the GMR deriva tive) is accurately predicted from a fluctuation-dissipation relation using the out-of-phase GMR in an ac field. A second noise mechanism, c onnected with defects in the antiferromagnetic order but not related t o overall magnetization fluctuations, was found near zero field.