The fundamental Barkhausen noise generated by the magnetization reversal of individual particles within a particulate magnetic medium has been observed using the anomalous Hall effect (AHE) as a sensitive magnetization probe. This is the first time the reversal of individual interacting single or nearly single domain particles has been detected. The jumps correspond to magnetic switching volumes of approximately 3*10/sup -15/ cm/sup 3/ with moments around 10/sup -12/ emu. The magnetization in a Co-Cr thin film, a columnar perpendicular magnetic recording medium, is determined by passing a current through the film and measuring the AHE voltage induced within the sample itself. Hall samples as small as 0.6 mu and containing only a few hundred columns have been made via microlithography. For these samples, the voltage change due to the reversal of a single column can be readily detected with a system sensitivity of 4*10/sup -14/ emu. The spatial dependence of the measurement response over the surface of the Hall geometry has been determined by both calculation and experiment, so that the magnitude of magnetization changes detected by jumps in the AHE voltage can be adjusted for geometric effects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
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Webb et al. (1988) studied this question.