Effect of Stress-induced Magnetic Anisotropy on the Properties of Giant Magnetostrictive Single Layer and Multilayer Thin Films

Abstract

Giant magnetostrictive thin films deposited on nonmagnetic substrates can constitute effective sensors and actuators for microdevices. In this work, we investigated the effects of a stress-induced anisotropy on the magnetic properties of Tb0.4Fe0.6, Fe0.5Co0.5 single layer films and [Tb0.4Fe0.6/Fe0.5Co0.5]n multilayers deposited on Si substrates. The magnetostrictive thin films were fabricated by means of RF sputtering and were subjected to a post-deposition annealing treatment. The uniaxial magnetic anisotropy was induced by bending the substrate before deposition and then allowing it to resume its original flat shape after depositing the film. The heat treatment was performed in a vacuum system with a vacuum of 10−6 Torr. The magnetic properties of the fabricated specimens were measured using a SQUID. SEM and XRD analyses were performed to ensure that the thermal treatment would relax the internal stresses induced during the deposition process without crystallizing the film. The thickness of the single layer thin films studied was between 300 and 800 nm while multilayer samples consisted of 6 layers with each layer thickness ranged from about 20 to 40 nm. Compared to single layer samples, multilayer samples with stress anneal growth exhibited an improvement in magnetic saturation by a factor of two while maintaining a low coercive field. Manipulations of the magnitude and direction of magnetic anisotropy was observed by introducing various values of tensile and compressive stress into the film.