Comments on "Improving accuracy of intrinsic coercivity measurement for magnetically soft materials"

The authors of the paper by Hilton et al. (see ibid., vol. 41. no. 8, P.2322-7, Aug. 2005) conclude among other things that "the commercial imperative is to obtain accurate coercivity results. How slow does the magnetizing field decay have to be in order to achieve this? There is no universal answer; it depends on the material and on the dimensions. For routine coercivity measurement of soft iron bars, a 60-s linear ramp time is advised. This protocol allows accurate coercivity measurement within an acceptable amount of laboratory time." The present author would like to mention that years ago a number of experiments were carried out indicating that coercivity of magnetically soft materials depends strongly on the rate of rise of the driving field. In the case of a linear ramp driving held, the coercivity, depends linearly on the square root of this rate of rise, k/sub i/. It was shown experimentally that the above dependence holds also for soft ferrites and Permalloy cores as well as for magnetic thin films.