Domain Theory of Ferromagnetics Under Stress Part II. Magnetostriction of Polycrystalline Material

Abstract

From the general formulas of Part I, expressions are derived for the magnetostriction of polycrystalline iron and nickel when the domains are isotropic, and when they are crystalline and have [111] or [100] as the direction of easy magnetization. The effect of assuming uniform strain rather than uniform stress is discussed. For iron at room temperature the experimental data fit the theoretical curve over a limited range; the deviations at high and low magnetizations can be explained qualitatively. For nickel at temperatures from 6°C to the Curie point, excellent agreement is found between theory and experiment. The analysis indicates that for the specimen studied, the domains are polycrystalline at low temperatures, but become smaller than the crystals at a little below 200°C, where the direction of easy magnetization becomes [100]. From the measurements at the higher temperatures, values are obtained for the saturation magnetostriction of nickel crystals magnetized in the [100] direction; from these and the saturation magnetostriction of polycrystalline nickel, values for the [111] direction are calculated.