在本研究中，主要探討奈米複合鐵磁/鐵電雙層膜的多鐵性效應。利用調整製程參數形成不同微結構與介電特性的鐵電薄膜，並研究不同介面粗糙度之鎳鐵(Ni80Fe20)/鈦酸鋇(BaTiO3)與鎳鐵/鈦酸鍶鋇(BaxSr1-xTiO3)雙層膜結構中的磁電耦合機制。鐵電鈦酸鋇材料具壓電性而非線性順電鈦酸鍶鋇材料在相變點有極大的介電常數改變。藉由觀察在鐵電居里溫度附近時磁性的改變，以探討雙層膜介面對多鐵性的影響。
鈦酸鍶鋇鐵電薄膜在550℃退火溫度以上與薄膜厚度90 nm以上時為良好多晶結構，並且極化特性隨退火溫度增加而改善。表面介電常數除受晶相影響外，亦隨應力增強。鎳鐵/鈦酸鍶鋇雙層膜在粗糙度較大的薄膜，具有優良的多鐵性耦合，主要藉由磁電感應產生，在鐵電居里溫度附近有∆M=2 emu/cm3的磁化量改變；而鎳鐵/鈦酸鋇雙層膜則由於有較大的電致伸縮效應，實驗觀察具有更強的多鐵性，在鐵電居里溫度附近有∆M=14 emu/cm3的磁化量改變。

In this study, the multiferroic properties of ferromagnetic/ ferroelectric bilayer nano-composites were investigated. Ferroelectric films with different microstructures and dielectric properties were obtained by controlling the sputtering parameters. To discuss the magneto-electric coupling mechanisms, Ni80Fe20/BaTiO3(BTO), and Ni80Fe20/BaxSr1-xTiO3(BST) bilayer structures were both fabricated to possess smooth and rough interfaces. The dielectric constant of the nonlinear paraelectric BST varied significantly during the phase transition, while the ferroelectric BTO has high piezoelectric constant. The interface effect on the multiferroic properties are thus revealed through the change of magnetic properties when scanning through the ferroelectric Curie temperature.
When the ferroelectric films were annealed above 550℃ and deposited thicker than 90 nm, superior polycrystalline phases were exhibited. The polarization of the films was also improved with higher annealing temperature. Surface dielectric constants were not only affected by the crystal phases, but also increased with the compressive strains. NiFe/BST bilayer structures with rough interface had good multiferroic couplings, which is mainly through the electric-magnetic induction. The variation of magnetization ∆M~2 emu/cm3 is observed in the NiFe/BST film near the ferroelectric Curie temperature. In contrast, due to the large electrostriction coefficient in BTO, the NiFe/BTO bilayer with rough interface had even better multiferroic properties. The robust variation of magnetization ∆M~14 emu/cm3 is obtained.

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