Irreversible Magnetic Effects of Stress

When Rayleigh's law for small hysteresis loops is interpreted in terms of the elementary process of domain wall displacement, its generalization to include effects of stress becomes possible. In this way theoretical formulas have been derived for the behavior of a soft iron or steel specimen which is first put into a state of normal magnetization at small magnetizing force $H$ and is then subjected to a small tension cycle. According to the theory the magnetization should increase upon application of tension $T$ by an amount $g(4.00\mathrm{}\times {10}^{-9\mathrm{}}HT+9,86\mathrm{}\times {10}^{-18\mathrm{}}{T}^2)$ in c.g.s. e.m.u., where $4\pi g$ is the slope of the normal permeability vs. $H$ curve, and should remain at the new value upon removal of the tension. An experimental test of the theory verified these predictions within the precision claimed for them. On the basis of the theoretical model, certain effects of diminishing alternating fields and stresses are analyzed quantitatively; the results are used to explain qualitatively the observed long-time magnetic behavior of ships.