Negative Anhysteretic Susceptibility, Internal Fields, and Domain Wall Interaction in Tape-Wound Cores of 50%–50% NiFe

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Abstract
Tape-wound cores of grain-oriented 50%–50% NiFe were studied in this investigation. The internal field generated by the sample was measured by means of anhysteretic magnetization curves. It was found that, in some cases, the internal field was regenerative, i.e., of the same polarity as the average magnetization. In some cases both a regenerative field and a degenerative demagnetizing field could be separately observed. The demagnetizing field is not a linear function of flux. If the internal field is regenerative, the anhysteretic susceptibility is negative. In order to measure negative anhysteretic susceptibility it is necessary to control the flux of the sample and measure the required magnetomotive force rather than vice versa. Otherwise one measures a spurious infinite susceptibility. A regenerative internal field explains the tendency of minor loops, for some cores, to drift away from the center of the major loop and into plus or minus saturation (``minor loop drift''). This is shown to be a case of positive feedback in which the loop gain exceeds unity and the system is unstable. The regenerative internal field is shown to be the result of magnetostatic interaction between pole-bearing domain walls. The internal field is not a single-valued function of flux, but depends on the detailed magnetization pattern of the sample. The characteristic field of the interaction is of the order of several A/m. The characteristic length is of the order of 10 m.

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