Liquid Phase Epitaxy of Ferromagnetic-Piezoelectrics Heterostructures and Femto-Tesla Magnetic Sensors and Arrays

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A research program is proposed on novel piezoelectric-ferromagnetic heterostructures for miniature, low-frequency, femto-Tesla magnetic sensors and sensor arrays with potential for applications in biomedical imaging. A majority of such magneto-electric (ME) composites studied so far have bonded ferroelectric and ferromagnetic layers in which an applied ac magnetic field produces magnetostrictive strain in the ferromagnet, leading to a voltage response in the ferroelectric layer. Ferroelectrics based ME sensors have several shortcomings including non-linear sensor response and considerable noise due to ferroelectric hysteresis and pyroelectric noise. This proposal is aimed at magnetic sensors made of piezoelectric lanthanum gallium tantalate, La3Ga5.5Ta0.5O14 (LGT), and functionally graded ferromagnetic layer with nickel zinc ferrite Ni1-xZnxFe2O4 (NZFO). The motivation is the group's preliminary data on ME effects in LGT-ferromagnetic composites that show (i) one to two orders of magnitude higher ME coefficients at low-frequency and at bending and electromechanical resonance, and much lower noise compared to samples with ferroelectrics, and (ii) theoretical models that predict a strong zero-bias ME interactions in the heterostructures. Intellectual Merit:The novelty in the planned approach is multifold with: (i) use of piezoelectric LGT that is expected to show strong ME coupling, linear voltage response to ac magnetic field and elimination of pyroelectric noise, (ii) graded ferromagnetic layers for self-magnetic biasing; (iii) heterostructures by liquid phase epitaxy (LPE) for efficient strain transfer; and (iv) utilization of micro-electro-mechanical systems (MEMS) technology in miniaturization of sensors and sensor arrays. Primary tasks will include (i) synthesis of magnetization-graded NZFO films on LGT substrates by liquid-phase epitaxy (LPE), (ii) studies on low-frequency and resonance ME interactions, (iii) design and fabrication of MEMS cantilever based ferrite/LGT multiple structures as resonant frequency tunable magnetic sensors and sensor array, (iv) comprehensive characterization of the materials and sensors. The desired fT-sensitivity will be achieved by frequency modulation with the sensor operating at bending or electromechanical resonance. Broader Impacts:Anticipated broader impacts of the research include the following: (i) Miniature magnetic sensors and sensor arrays for applications in diverse fields, including medical imaging (magneto-cardiography and magneto-encephalography) and security systems. (ii) Human resources development and curriculum development/enrichment in materials and measurement technologies. (iii) Undergraduate Research Training: The PIs will recruit undergraduate science and engineering majors for participation in the research. (iv) Research experience for high school students: Students from local schools will be recruited for participation in research.