Fundamental Investigations and Industrial Applications of Magnetostriction

Abstract

So far only bulk materials are used for technological applications of magnetostriction. For applications in micro-systems technology magnetostrictive films have to be developed, which show excellent soft-magnetic properties combined with giant magnetostriction. Amorphous Tb-DyFe films, which are prepared possessing an in plane or transverse magnetic anisotropy, show excellent soft-magnetic properties combined with giant magnetostriction. However, for technical applications the major drawback is the low Curie temperature which is typically around 400 K. To increase the Curie temperature and simultaneously achieve good soft-magnetic properties as well as giant magnetostriction the preparation of crystalline films with nanometer-sized grains is necessary. Terfenol-D-like films with additives of Zr or Mo were prepared by ion beam sputtering and different heat treatments were applied to investigate the crystallization behaviour. Furthermore, nanometer-scaled multilayers with Nb interlayers were prepared. This multilayer structure is suitable to inhibit grain growth and hence further decreases the average grain size. The resulting nanocrystalline microstructure leads to small coercive fields and high Curie temperatures. In addition, protective layers were investigated in order to avoid oxidation during the heat treatments for crystallization. The results will be discussed with respect to possible applications in micro-system technology. For industrial automation the actuation with compressed air plays an important role since pneumat-ics has without doubt always been an ideal modular system for all kinds of applications in almost every field of technology. Owing to its high modularity pneumatics is constantly complemented and expanded by new technological developments, such as proportional pneumatics and servo-pneumatic actuators. Beside developments to evaluate the possibilities to use solid state actuators for miniaturized valves, already extremely accurate contactless displacement sensors on the basis of magnetostrictive effects are used for applications mentioned above. These magnetostrictive displacement sensors are detecting the propagation delay time of an ultrasonic wave in a mag-netostrictive tube created by the interchange of a longitudinal and a circular magnetic field, the so-called Wiedemann effect. The principle of the Wiedemann effect will be explained and recent developments in utilizing this effect for highly sensitive position sensors will be shown.