| Results are presented for a series of studies performed to improve the understanding of the interactions observed in giant magnetostrictive (GMS) materials and to increase the capability to design effective film-substrate (bimorph) structures intended for microdevices. First, some of the most important achievements made in the process of understanding, modeling, fabricating and using GMS materials in bimorph systems are summarized. Next, the inconsistencies found in the solutions obtained by previous authors for the problem of finding the strains observed in magnetostrictive materials that are subjected to an arbitrary uniaxial stress, or that are in the form of thin films deposited on nonmagnetic substrates are examined. The origin of the inconsistencies is identified and more general and self-consistent solutions are proposed. Using these solutions, the static strains, stresses, energy densities and the bending and twisting deflections that can be magnetostrictively induced in bimorph beams and plates are calculated. The resulting expressions are used to derive the conditions that define film-substrate cantilevers that show maximum deflection, as required in the case of sensors, or that exert maximum force, as required in the case of actuators. Having the capability to calculate strains and stresses in GMS materials, the effect of a stress bias which is created by bending the substrate during the deposition of a magnetostrictive multilayer is studied. In particular, the orientation of the easy axis, the uniaxial anisotropy energy, the anisotropy field, and the magnetization along various hard axis directions when an external magnetic field is applied in those directions are obtained. Finally, a model that can be used to calculate the natural frequencies of vibration of film-substrate systems and to predict their dynamic response to the application of variable magnetic fields is presented. The calculation schemes proposed in this work are suitable for generalization to the cases in which the deformation of bimorph beams and plates is produced not only due to magnetostriction in the films, but also due to thermal, piezoelectric or hygroscopic strains. All the expressions obtained can be used regardless of the relative magnitude of the thickness of the film compared to the substrate. |
