White-noise magnetization fluctuations in magnetoresistive heads

Thermal magnetization fluctuations in magnetoresistive (MR) heads for magne tic hard-disk storage are a fundamental limit on their signal-to-noise rati o. The resultant noise is essentially frequency flat (white), scales with h ead sensitivity as signal does, but increases inversely with sensor volume. It will impact the present course of industrial R&D efforts toward geometr ic scaling and increasing raw head sensitivity to achieve increased areal s torage densities and data rates. Magnetization noise is shown to exceed Joh nson noise in 0.4 mum sensor size, giant-MR spin-valve heads designed for s imilar to 20 Gbit/in.(2) areal storage density. The basic physics underlyin g the experimental results is shown to be consistent with predictions from the fluctuation-dissipation theorem. (C) 2001 American Institute of Physics .