Development of Magnetostrictive Fe-Co-B Alloys for High-frequency Sensors and Magnetoelectric Composites
Type of DegreeDissertation
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Magnetostrictive materials with soft magnetic properties have been widely used in sensors, resonators, actuators and transducers. For high-frequency biosensor applications, the miniaturization of these devices is necessary. Commercial, soft-magnetic amorphous materials have been used for biosensors, however, it is still challenging to fabricate them at micro/nano scale for higher frequency applications. Thus, it is necessary to find new materials with easy fabrication at micro/nano scale and suitable structure, properties, and novel sensor behavior. In this research, Fe-Co-B alloys have been proven to be good candidates. Among Co-rich, equiatomic Fe and Co, and Fe-rich Fe-Co-B alloys, Fe-rich alloys are found to have the best resonant behavior. Amongst the films with solution composition of Fe57Co29B14, Fe55Co28B17, Fe53Co27B20, Fe51Co26B23 and Fe49Co25B26, magnetostrictive particles (MSPs) from solution composition of Fe55Co28B17 exhibit the best resonant behavior. In this research, the influence of deposition time, Na Saccharin, and current density on the structure, morphology, and resonant behavior of film with solution composition of Fe55Co28B17 are mainly studied. To better understand the role of Fe and Co in the ternary alloys, binary alloys with solution composition of Fe55B17 and Co28B17 were fabricated with the same deposition parameters as ternary alloys with solution composition of Fe55Co28B17. By reducing the Co content, higher Fe/Co ratios were achieved. The structure, morphology, resonant behavior and magnetic properties of Fe-Co-B alloys with different Fe/Co ratios were compared. The Boron influence was studied on films with solution composition of Fe55Co16Bx (x=0~29) and Fe55Co24Bx (x=0~29). Au/Fe-Co-B/Au MSPs in micro size were fabricated by combining electrodeposition and microfabrication methods. The morphology and resonant behavior of the MSPs were characterized. Au/Fe-Co-B/Au MSPs were used to detect Salmonella Typhimurium. The measurement sensor shows a limit of detection of 5×102 cfu/ml with a total peak shift of 107 kHz in the dynamic measurement. Fe-Co-B/PVDF magnetoelectric composites were fabricated by electrodepositing a Fe-Co-B thin film on a PVDF film. The magneotelectric (ME) effect of the composites was characterized in cantilever mode and probe mode. The ME coefficients of composites with different lengths and thicknesses were compared.