Fluctuation-dissipation relation for giant magnetoresistive 1/f noise

We find that Co/Cu multilayers exhibiting giant magnetoresistance (GMR) also show giant magnetoresistive 1/f noise. The largest component of this noise (which peaks at magnetic fields maximizing the GMR derivative) is accurately predicted from a fluctuation-dissipation relation using the out-of-phase GMR in an ac field. A second noise mechanism, connected with defects in the antiferromagnetic order but not related to overall magnetization fluctuations, was found near zero field. © 1993 The American Physical Society.