Demagnetizing factors for disk samples of nonideal soft magnetic materials

To find out whether experimental magnetometric demagnetizing factors for disk samples of permalloy are valid for other magnetic materials with significant values of coercive field, we measured demagnetizing factors for disk samples of 1095 (high carbon) steel shim stock (H(c) congruent to 45 Oe), and for cold-rolled pure nickel (H(c) congruent to 23 Oe). The observed demagnetizing factors for steel agree well with those for permalloy but the values for cold-rolled nickel do not, at least for disk samples with diameter-to-thickness ratios d/t greater than 100. The criterion for agreement appears to be a hysteresis loop (M versus H) with straight, parallel sides up to at least half the saturation magnetization, implying a magnetization process controlled by the magnitude of the demagnetizing field. (C) 2010 American Institute of Physics. [doi:10.1063/1.3347916]