The origin of Barkhausen noise in small permalloy magnetoresistive sensors

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Abstract
The magnetoresistive (MR) response of permalloy sensors is increasingly plagued by jumps or noise of a magnetic origin (so‐called Barkhausen noise) as their sizes are reduced to tens of microns. The origin of this noise is not presently understood. In previous work (1) we reported a study of the Barkhausen noise by separately measuring the MR response and the domain processes involved, but detailed correlation between the two was still lacking. In this work, therefore, we performed simultaneous measurements of both the MR response and domain patterns on small MR elements of typically 12μm×24μm, enabling us to analyze the domain processes affecting the MR output. We have identified two classes of domain processes primarily responsible for noise in the MR output, namely, abrupt domain wall population reductions during early stages of demagnetization, and wall state transitions involving nucleation and expansion of N− wall segments around zero field. Additional insight into the N+→N− transitions has been obtained through consideration of the energetics of formation of the N− segment, and the response of such a segment to applied fields.

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