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Sample-Shape Dependence of Zero-Field Magnetic Noise

A fluctuation-dissipation-theorem derivation showing that the shape of a magnetic sample rescales its zero-field noise autocorrelation function: for monotonically relaxing noise the amplitude and mean relaxation time each drop by a factor 1 + N*chi_i (demagnetizing factor times intrinsic susceptibility), suppressing the zero-frequency power spectrum by (1 + N*chi_i)^2, which yields experimental tests of the FDT distinguishing bulk from surface effects.

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Sample shape dependence of magnetic noise Steven T. Bramwell1

This theoretical paper explains why zero-field magnetic noise, characterised by the magnetic autocorrelation function Ss(t), depends on the shape of the sample. Starting from the fluctuation-dissipat…