"Ni-Mn-Ga Thin Film Structures for Microactuation"

Ferromagnetic shape memory alloys (FSMAs) represent a new type of multifunctional smart materials that exhibit a giant magnetostrain effect, MSE, (10% in a field lower than 1 T) alongside the ordinary shape memory effect and superelasticity. These appear as a result of magnetically driven twin variant reorientation in the tetragonal or orthorhombic martensitic phase or thermally / stress/magnetic field- induced martensitic transformation (MT).

In this work, we will present the details of thin film technology of FSMAs developed at UPV/EHU.  A magnetron DC sputtering of the in-house fabricated Ni-Mn-Ga targets on heated at 500 C substrates is used to facilitate a formation of 5M- or 7M-martensitic phases in the films at room temperature. Sputtering parameters like power, Ar pressure and substrate temperature were optimized to obtain the desired composition and proper microstructure. The transformation characteristics and functional properties of the prototype thin films (typically 1 micron-thick) epitaxially grown on MgO(100) were studied by XRD, thermomagnetization and resistivity curves, AFM/MFM and dynamical mechanical analysis (DMA).

Design and fabrication of freely movable Ni-Mn-Ga microstructures for micro-scale actuation  was probed by using arrays of Ni-Mn-Ga/Si(100) cantilevers with a different aspect ratio prepared by using electron beam lithography (EBL), ion beam etching (IBE) and a Cr based sacrificial layer technology.

The first results of their mechanical and magneto-mechanical  performance will be presented.