Ni-Mn-Ga is a ferromagnetic shape memory alloy that can be used for future
sensors and actuators. It has been shown that magnetic field can induce phase
transformation and consequently large strain in stoichiometric Ni2MnGa. Since then
considerable progress has been made in understanding the underlying science of shape
memory and ferromagnetic shape memory in bulk materials.
Ni-Mn-Ga thin films, however is a relatively under explored area. Ferromagnetic
shape memory alloy thin films are conceived as the future MEMS sensor and actuator
materials. With a 9.5 percent strain rate reported from magnetic reorientation, Ni-Mn-Ga thin
films hold great promise as actuator materials.
Thin films come with a number of advantages and challenges as compared to
their bulk counterparts. While properties like mechanical strength, uniformity are much
better in thin film form, high stress and constraint from the substrate pose a significant
challenge for reorientation and shape memory behavior. In either case, it is very
important to understand their behavior and examine their properties. This thesis is an effort to contribute to the literature of Ni-Mn-Ga thin films as ferromagnetic shape
memory alloys.
The focus of this project is to develop a recipe for fabricating NiMnGa thin films
with desired composition and microstructure and hence unique properties for future
MEMS actuator materials and characterize their properties to aid better understanding of
their behavior. In this project NiMnGa thin films have been fabricated using magnetron
sputtering on a variety of substrates. Magnetron sputtering technique allows us to tailor
the composition of films which is crucial for controlling the phase transformation
properties of NiMnGa films. The composition is tailored by varying several deposition
parameters. Microstructure of the films has been investigated by X-ray diffraction
(XRD) and transmission electron microscopy (TEM) techniques. Mechanical properties
of as-deposited films have been probed using nano-indentation technique. The chemistry
of sputtered films is determined quantitatively by wavelength dispersive X-ray
spectroscopy (WDS). Phase transformation is studied by using a combination of
differential scanning calorimetry (DSC), in-situ heating in TEM and in-situ XRD
instruments. Magnetic properties of films are examined using superconducting quantum
interface device (SQUID).
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-08-8271 |
| Date | 2010 August 1900 |
| Creators | Jetta, Nishitha |
| Contributors | Zhang, Xinghang |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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