The Significance of Magnetostriction in Permalloy

Magnetostriction in permalloy, measured by McKeehan and ${\mathrm{C}\mathrm{i}\mathrm{o}\mathrm{f}\mathrm{f}\mathrm{i},}^1$ confirms qualitatively the existence of atomic magnetostriction, as previously proposed, and the explanation, based thereon, for high magnetic permeability and low hysteresis in these alloys. The effect of tension upon magnetostriction suggests that orientation of the magnetic axes of iron and nickel atoms precisely like that due to the application of magnetic fields may be effected by mechanical stresses within the elastic limit. Acceptance of this view makes it possible to explain the large effects of tension upon magnetic hysteresis and the observed relation between the changes in electrical resistance produced by tension and by magnetization. The occurrence of a reversal of magnetostriction in a stretched wire containing 80 percent Ni is covered by the same explanation. A connection between magnetic hysteresis and mechanical hysteresis is suggested and the molecular field postulated by Weiss is interpreted as the integrated effect of local mechanical stresses.