Modeling of thermal magnetization fluctuations in thin-film magnetic devices

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Abstract
It has been recently shown that broad-band, thermally induced magnetization fluctuations in submicron magnetoresistive (MR) read sensors (used in all present and foreseeable magnetic hard-disk-drives), will serve as a fundamental limit to their achievable signal-to-noise ratio, independent of how large the intrinsic sensitivity parametrics, e.g., ΔR/R, may be. This type of magnetization noise may also be of consequence and/or interest for a broader class of future nanoscale magnetic devices. The foundation for understanding and quantitatively modeling this phenomenon on a practical device-physics level is the fluctuation-dissipation theorem (FDT). This paper develops a theoretical methodology for application of the FDT to the problem of micromagnetic modeling of thermal magnetization fluctuations in small, magnetically soft thin-film magnetic devices, using a generalized Gilbert formulation of magnetization dynamics with phenomenological damping.