Direct Current Hysteresis Loops of a MuMETAL Ring Measured by Continuous Recording and Automatic Ballistic Methods

We measured saturated hysteresis loops of a MuMETAL ring using a computerized, high-resolution apparatus by both extrapolated continuous recording and automatic ballistic methods. The recording time per loop varied from 17.7 to 141.6 s. The loops obtained for short recording times were significantly wider than the loop obtained by the ballistic method. By extrapolating the magnetic field of different loops at the same flux density values linearly to zero flux density rate, the resultant dc loop had coercivity in agreement with its ballistic value. The results are quantitatively analyzed and discussed on the basis of eddy current models. The intolerably large variation and bias in the measured coercivity stated in a current ASTM standard may be resolved by this technique.