Although, Terfenol-D rods are manufactured with the magnetic moments nearly perpendicular to its axis, a static stress (mechanical preload) is must for achieving full alignment of all the moments. The stress and isotropy generated by the static compression (or tension in the case of materials with negative magnetostriction) enhances the overall magnetoelastic state of the material [Figure 29.1]. A mechanical preload also adds to the cause as it helps in avoiding operating the rod in tension, particularly when driving brittle material such as Terfenol-D at/or near mechanical resonance.

There has been a resurgence of interest in MS materials during the last decade primarily due to the commercial availability of the rare-earth iron compounds capable of producing large quasi-static strains of over 1600 µstrain in response to moderate magnetic field of 160kA/m. The most technologically advanced of these compounds is the alloy Terfenol-D, Tb_0.3Dy_0.7Fe_1.92 , which has become the primary MS material for transducer applications. Terfenol-D exhibits a combination of high single crystal magnetostriction and low magneto-crystalline anisotropy. Since magnetostriction is an inherent material property, it does not degrade over time. More importantly, Terfenol-D layers can easily be embedded into laminated composite structures without significantly affecting their structural integrity.