Research On Preparation And Properties Of FeCo/PZT Magnetoelectric Laminated Composites

ME composite materials, particularly layered ME composites, show strong ME coupling atroom temperature. ME composites with complex shape and configuration attract a lot of attentionfor their special ME properties. To enhance the ME effects, classical laminate ME composites areformed by one piezoelectric layer placed between two positive or negative magnetostrictive layers.It has been proved that the magnetostrictive layers with opposite signs of magnetostriction canprovide effective excitation of the bending acoustical oscillations and enhanced the ME coupling.Therefore, the ME effects of negative magnetostrictive/piezoelectric/positive magnetostrictivestructures need further research.The structure, magnetization and magnetostrictive properties of FeCo layers prepared byelectroless deposition were studied in this thesis. Large ME effects have been obtained inFeCo/PZT/FeCo cylindrical composites in which the magnetosrrictive layers are in direct contactwith the piezoelectric layers. The ME voltage coefficient of FeCo/PZT/FeCo increases and theresonance frequency decreases as the cylinder diameter increases. The ME effects have beeninvestigated in Ni/PZT/Ni, FeCo/PZT/FeCo and Ni/PZT/FeCo trilayered cylindrical compositesand Ni/PZT/FeCo trilayered arc-shaped one obtained by electroless deposition. Compared to thosein the Ni/PZT/Ni and FeCo/PZT/FeCo cylinders with the same configuration, the ME voltagecoefficient of the Ni/PZT/FeCo cylinder increases by68%and45%. It indicates that the MEvoltage output of cylindrical ME composites with negative magnetostrictiv/piezoelectric/positive magetostrictive structure can be efficiently enhanced by the overall compressive stress onthe piezoelectric layers induced by the inner and outer magnetostrictive layers of the cylinder. Forthe FeCo/PZT/FeCo and Ni/PZT/FeCo cylinders, the ME voltage coefficient increases and theresonance frequency decreases as the cylinder diameter increases. The ME behavior of theNi/PZT/FeCo is different from those in previous studies and zero-bias ME effects and fourremarkable resonant peaks have been observed in the dependence of the ME voltage coefficient onthe magnetic field frequency in the1-150kHz range. The zero-bias and multi-resonant-frequencyME effects are expected to be used in related multifunctional devices.