The proposed research focuses on structured analytical and experimental analysis of magnetostriction in iron-gallium (Galfenol) thin films and nanowires to advance understanding of the magnetostrictive physics at this scale and to enable transformative new micro- and nano-scale device functionality. This alloy system has the distinct advantage of having high strains in response to magnetic fields (400ppm) while also exhibiting the mechanical ductility and strength of iron. The ability to electrodeposit this active material is possible due to preliminary work which overcame the difficulty of Ga oxidation in aqueous electrolytes, and which therefore enabled FeGa metallic alloys to be fabricated as thin films and nanowires.
The intellectual merit of this research includes that insights from study of the proposed micro- and nano-scale test devices will lead to a deep understanding of the exciting device physics needed to facilitate utilizing magnetostriction at the nanoscale such as in artificial cilia sensors and actuators that mimic biological transducers in nature. As the only highly responsive material possible as ductile nanowires and conformal (nonplanar) thick films, this research is also expected to lead to the creative, new concepts for transformative sensors and actuators at the micro- and nano-scale. This work proceeds with an original plan to make the leap from materials science to devices with four important goals. The first goal is a simple, yet critical, step of measuring magnetostriction of electrodeposited Galfenol thin films as a function of composition, crystallographic orientation and magnetic domain orientation. A capacitance bridge will be used to measure the magnetostriction of these films and the optimal deposition parameters will be used in the subsequent goals. The second goal is to make a non-contact torque sensor as a test device to study the device physics of Galfenol films. The torque sensors will be evaluated in an existing rotating shaft torque test stand. The third goal involves high-risk, high-payoff measurements of magnetostriction in nanoscale devices (10-100nm diameter Galfenol nanowires). Wires with the right composition, crystal structure, and even necessary segmentation have been previously made, but measuring magnetostriction at this scale is difficult due to unknown strains, very small magnetic fields (from single wires), and general size constraints. Here, measurements of giant magnetoresistance (GMR) in individual nanowires will be used to determine the effect of applied tensile and compressive strains. In addition, magnetic force microscopy will be used to observe magnetization rotation in bent nanowires to verify GMR results. The fourth and last goal will involve making high-resolution tactile sensors using Galfenol nanowires to learn more about their behavior and integration into devices.
This research will have impact in a broad variety of fields including spintronics (FeGa on GaAs), vibration sensors, energy harvesters as cantilevers and/or nanowires, and a wide range of sensors and actuators using non-contact mechano-magneto coupling (e.g. conformal non-contact torque sensors and structural health monitoring sensors). This research will impact the education of undergraduates via REU programs at both universities, and especially underrepresented students via faculty mentoring programs. Graduate students will benefit from course development that will include the research results from this project and from interactions with industry via industrial centers with annual reviews, journal clubs, and seminars. Finally, the PIs' will train students in outreach to k-12 students to continue the broad impact in the next generation.
