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).

"The structural, thermal, magnetic, and mechanical properties of Ni-Mn-Ga magnetic shape-memory alloys depend strongly on composition. Compositions of sputter deposited films differ from the composition of the single alloy targets from which they originate, where the composition change depends on sputter parameters. Films produced via physical vapor deposition from single alloy targets have sound film-substrate adhesion and film uniformity, however, accurate control of composition is difficult. Tri-sputter deposition from multiple targets allows the flexibility of varying deposition rates and film compositions. A robust procedure with three targets (nickel, nickel-gallium, and manganese) was developed to deposit Ni-Mn-Ga films on silicon with defined composition, structural and magnetic properties. The sputter power was controlled and varied independently and systematically for each target. A film with a targeted composition of Ni50Mn28.6Ga21.4 at. % Energy-Dispersive X-ray Spectroscopy (EDS) yielded the composition Ni50.5Mn29.2Ga20.3 at.-%. X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) revealed the 14M modulated martensite structure, a fiber texture, an average grain size of approximately 100 nm. The martensitic start and finish temperatures, measured with multi-beam optical sensor wafer curvature deflectometry, were 122 °C and 81 °C respectively, indicating stress-induced martensite formation at high temperature. Tri-deposition using three targets provides a method to control composition of Ni-Mn-Ga films and adjust film properties such as martensite structure and transformation temperature via target power adjustment."--Boise State University ScholarWorks.

This book, the first dedicated to this exciting and rapidly growing field, enables readers to understand and prepare high-quality, high-performance TiNi shape memory alloys (SMAs). It covers the properties, preparation and characterization of TiNi SMAs, with particular focus on the latest technologies and applications in MEMS and biological devices. Basic techniques and theory are covered to introduce new-comers to the subject, whilst various sub-topics, such as film deposition, characterization, post treatment, and applying thin films to practical situations, appeal to more informed readers. Each chapter is written by expert authors, providing an overview of each topic and summarizing all the latest developments, making this an ideal reference for practitioners and researchers alike.

Ni-Mn-Ga thin films have attracted significant attention over the past two decades due to its multifunctional properties, leveraging these characteristics in applications such as actuators, sensors, and micro-electromechanical systems (MEMS). The most favorable deposition technique for making Ni-Mn-Ga thin films is magnetron sputtering where the target used is near stoichiometric Ni2MnGa alloy. Ni-Mn-Ga alloy target manufacturing has been challenging and costly due to design constraints, process optimization issues and inefficient target utilization resulting in compounded negative economics. To address these problems, this research aimed at investigating and demonstrating the viability of a cost-effective, modern technology known as binder jetting additive manufacturing (BJAM) technique to produce targets with excellent target consumption efficiency based on proposed target design. The additive manufactured Ni-Mn-Ga alloy target process began with ball-milled Ni-Mn-Ga powder having bimodal particle distribution to ensure an increased packing density and mechanical strength after the determination of optimized 3D printing parameters. The printed targets were post-processed through curing, de-binding and sintering. Sintering was conducted in an inert/argon atmosphere to safeguard essential material properties which were benchmarked through characterization. Backscattered electron (BSE) micrographs showed AM targets were homogenous with martensitic twin microstructures necessary for shape memory behavior. The XRD results showed that the martensitic twin microstructures were mostly tetragonal and monoclinic crystal structures. The martensitic transformation temperatures for Ni-Mn-Ga targets ranged from 79.3 to 148.1°C and possessed a maximum density of 87.18%. Using the direct current (DC) magnetron sputtering, Ni-Mn-Ga thin films were deposited on Si (100) substrates at discharge currents ranging from 0.05 to 0.15 A and substrate temperatures 20°C to 700°C. The effect of discharge current and substrate temperature on surface morphology, composition, crystal structure of Ni-Mn-Ga thin films on silicon substrates were investigated. As the discharge current increased, the film showed increased grain size. The grain morphology, as appeared from the investigation of the film planar surface was of elongated grains. The film crystallinity also increased with increased discharge current, as proved by XRD investigations. The most important effect of maintaining the discharge current value constant and increasing the substrate temperature was the change in chemistry and crystallography of the obtained Ni-Mn-Ga thin films. The film deposited at 700°C showed the closest chemical composition to the target composition. For the other substrate temperatures, the high oxygen contamination, due perhaps to not-so-optimum deposition conditions, drastically altered the film composition. By increasing the substrate temperature, the film crystal structure changed from Heusler L2I cubic (high temperature phase) to monoclinic (low temperature phase). It was also demonstrated that, 3D printed sputtering targets of different geometrical designs are potential for improving target utilization efficiency and film properties.

This report comprises a selective survey of the present knowledge of the effects of occluded gases and strains on the magnetic properties of Permalloy films, particularlly those which have significance for computer switching applications. Other possible techniques for accomplishing future computer switching functions and magnetic film properties are reviewed. Bulk properties are described and compared with corresponding thin film properties. The magnetic properties of epitaxial Permalloy, epitaxial nickel, epitaxial iron, polycrystalline nickel, and polycrystalline iron films are discussed. The effects of various occluded gases on magnetic film properties are summarized. Stresses present in evaporated films and their significance in determining the magnetic properties of thin films are considered. A selected bibliography of 548 references is included. (Author).