The Effect of Strain on Magnetostriction and Magnetization in Nickel

With a heterodyne beat method, magnetostrictive hysteresis loops have been obtained for a nickel wire under three different tensions. Magnetic hysteresis loops for the same wire and same tensions were also secured. The magnetostrictive contraction, $\frac{\mathrm{dL}}{L}$, for the tensions 6.82 and 3.70 kg/${\mathrm{mm}}^2$ is given quite accurately by the one equation, $\frac{\mathrm{dL}}{L}=-1.93\mathrm{}\times {10}^{-10\mathrm{}} I^2$, where $I=\mathrm{intensity}\mathrm{of}\mathrm{magnetization}$. For a tension 0.72 kg/${\mathrm{mm}}^2$ the equation $\frac{\mathrm{dL}}{L}=-1.30\mathrm{}\times {10}^{-10\mathrm{}} I^2$ holds somewhat less accurately. The effect of compression and of stretch on the residual magnetization of a nickel wire in a demagnetizing field is determined experimentally. From this experiment, and from the magnetostriction curves, it is shown that at certain field strengths the magnetism of a nickel wire, bent elastically into a circular arc, becomes unstable. Thus the large discontinuities in the magnetization curve observed by Forrer may be explained. It is suggested that the small Barkhausen jumps of magnetization may be due to similar magnetic instability produced in small regions by local strains.