Physical properties of multidimensional and multiferroic composites

The properties of multidimensional and multiferroic composite systems consisting of smart materials are investigated for the intended use in microelectromechanical systems (MEMS) sensor and actuator applications. A multidimensional composite system combines within it different dimensionalities such as 1-D, 2-D, and 3-D constituents. A multiferroic composite system, meanwhile, consists of different ferroics such as ferroelastic, ferromagnetic and ferroelectric materials.; We demonstrate effects of dimensionality on thermoelastic properties of NiTi/Si cantilevers for MEMS actuators. The stress state of the bimorph cantilevers is controlled by the dimensionality of the Si cantilever surface (2-D or 1-D corrugated) or the NiTi thin film (2-D or 1-D patterned). Compared to single dimensional NiTi/Si cantilevers the multidimensional device features an improved actuation performance, that is, it combines a small thermoelastic with a large martensitic transformational deflection.; We also demonstrate magnetoelectric effects as examples of multiferroic composite systems for novel sensor applications. An example is the magnetic field induced magnetoelectric effect, ME_H, in a ferroelectric/ferromagnetic composite PVDF/Terfenol-D. Here, an applied magnetic field induces a piezomagnetic strain in Terfenol-D, which couples to PVDF and induces a piezoelectric charge or voltage. We obtained a ME_H coefficient of 1.43 V/cm Oe in agreement with an analytical calculation. The magnetoelastic coupling coefficient of the PVDF/Terfenol-D composite is estimated as 11%. Further, we demonstrate an electrical field induced magnetoelectric effect, ME_E, in the ferromagnetic/ferroelectric composites CoB/PZT and PZT/Metglas/PZT. In this case the application of an electric field induces a piezoelectric strain in the PZT ceramic. The strain couples to piezomagnetic CoB or Metglas. Hence, the magnetization of the ferromagnetic materials changes with the electrical field applied to the ferroelectric material. The ME_E coefficient was obtained, 0.025 Oe cm/V for CoB/PZT and −0.015 Oe cm/V for PZT/Metglas/PZT composites. Those ME_H and ME_E coefficients obtained for the composites are larger than those of naturally occurring multiferroic materials.