MODERN MAGNETOSTRICTIVE MATERIALS - CLASSICAL AND NON-CLASSICAL ALLOYS

摘要

Magnetostrictive materials have not changed greatly from their discovery by Joule in 1842 through the 1960's. Their saturation strains remained small and their magnetomechanical couplings were only moderate. The separation of the rare earth elements during World War Ⅱ and the subsequent measurement of their magnetic properties, created the groundwork for the development of "giant" magnetostrictive materials during the 1960's. Magnetically anisotropic Tb and Dy became the generators of unprecedented classical magnetostrictions of nearly 1%. Coupling factors increased to ～0.8. During the same period, a remarkable 5-fold increase of magnetostriction (λ_(100)) of commonplace b.c.c. Fe with concentrations of Al near18% was discovered. More recently, measurements in b.c.c. Fe-Ga alloys have shown a still greater enhancement of the magnetostriction, yielding strains of nearly 400 x 10~(-6) over the wide range in temperature from 4 K to far above room temperature. In the Fe alloys, as well as in the rare earth alloys, there is no known stress limit to the magnetostriction. Power output is limited by magnetic field generation and mechanical sample failure. Within the last few years, a new class of magnetostrictive materials, ferromagnetic shape memory alloys (FSMA's), have been introduced. These materials have huge magnetically induced strains (～5%). However, unlike the classical magnetostrictive alloys, these strains may be stress limited. While all the above materials have been introduced primarily for their high power electrical to mechanical energy conversion capability, they also function in the reciprocal mode, as magnetomechanical sensing materials.