Magnetostriction in Permalloy

The materials studied comprised iron, nickel, and permalloys containing 46, 64, 74, 78, 80, 84 and 89 percent nickel. The method permitted simultaneous measurement of magnetization and magnetostriction in about 12 cm at the middle of a 40 cm wire, 1 mm in diameter, in an approximately uniform field not exceeding 40 gauss, and either with or without applied tension (within the elastic limit).The magnetostriction was measured by a combination of a mechanical lever, an optical lever, a multiple slit and a photoelectric cell. The magnifying power of this combination, as used, was about 2×{}10⁶, and magnetostrictive strains from 2×{}10^-9 to 3×{}10^-5 were detected and measured without changing the sensitivity.The magnetostriction-magnetization curve has initial slope zero in all the cases studied. When the attainable field was sufficient for magnetic saturation the magnetostriction reached a limiting value. In iron there is evidence for the existence of a Villari reversal in fields too great to be attained in the apparatus. In nickel there is no sign of such reversal. In the permalloys with more than 81 percent Ni the magnetostriction is a contraction. In the permalloys with less than 81 percent Ni the magnetostriction is an expansion. The limiting values of magnetostriction, when plotted against chemical composition, fall on a smooth curve.Tension increases magnetostrictive contraction and diminishes magnetostrictive expansion. It causes a reversal in the sign of magnetostriction in permalloy with 80 percent Ni, a small contraction preceding the final small expansion.