The Influence of Grain Interaction on the Magnetostrictive Behaviour of a Single Crystal of Silicon-Iron in a Polycrystalline Matrix

Abstract

The magnetostrictive changes in length accompanying the rotation of a magnetic field, sufficiently high to give saturation, have been studied for diskshaped specimens of silicon-iron, using a strain-gauge technique. The measurements were made on specimens prepared from single crystals, which were grown by the Bridgman technique, and on individual crystals in polycrystalline samples. The values of the magnetostriction constants ?100(or 2h1/3) and ?111(or 2h2/3) for the 3% silicon-iron single-crystal specimens agree reasonably well with those reported previously. For rotation in the (110) plane from the [001] direction, the curve of saturation magnetostriction against angle of rotation from the [001] direction (the strain-gauge direction) for the single crystal is adequately described by single constant. It has been found that the magnitude of the curves for individual (110) crystals in a (110) matrix of grains with misalignment of the [001] directions is decreased, depending on the amount of misaligned material present. A simple theory, based on interaction between grains at their boundaries, has given good quantitative agreement with the results. As the amount of misaligned material around a crystal is increased, the saturation magnetostriction curve for rotation from the [001] direction in the (110) plane could no longer be described by a single constant, and it was necessary to include an additional term and a constant of increasing magnitude. This term represents the contribution of the volume magnetostriction to the linear magnetostriction, and it is reasonable to expect that, as the crystal is increasingly constrained, enhanced interaction should occur.