在本研究中，主要探討奈米複合雙層膜的多鐵性效應。利用調整製程參數形成不同成分與介電特性的鐵電薄膜，並研究不同鍶濃度參雜之鈦酸鍶鋇材料以及不同厚度磁性層中，鎳鐵氧/鈦酸鍶鋇的磁電耦合機制介。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，而不同成分比之鈦酸鍶鋇其相變溫度亦不相同，藉由觀察在鐵電居禮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。介面效應對於不同厚度其所占有整體效應不同，利用不同厚度的磁性層觀察其在鐵電相變溫度時磁性改變，以觀察介面效應對磁電耦合機制之影響。
鈦酸鍶鋇鐵電薄膜在不同比例時晶格常數不同。表面介電常數除受晶相影響外，亦隨應力改變。鎳鐵氧/鈦酸鍶鋇雙層膜應力逐漸減少時，其磁化量改變亦逐漸減少，顯示在磁電耦合效應中應力佔有相當重要的腳色。而在不同厚度磁性層系統中，可觀察到其磁化量改變量隨著磁性層厚度增加而減少，磁性層10 nm時磁化量變化量為25.46 emu/cm3，磁性層60 nm時磁化量變化量為0.16 emu/cm3。說明當磁性層達到一定厚度，其介面效應的影響降至可忽略的部分，所以其磁電效應不明顯。

In this study, the multiferroic properties of ferrimagnetic/ ferroelectric bilayer nano-composites were investigated. Ferroelectric films with different microstructures and dielectric properties were obtained by controlling the sputtering parameters. To discuss the magnetoelectric coupling mechanisms, NiFe2O4(NFO)/(Ba,Sr)TiO3(BST) bilayer structures were fabricated with various Sr concentration doping into BaTiO3. 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 at the ferroelectric Curie temperature.

The lattice constant of the BST films were different while the Ba and Sr ratio was changed. Surface dielectric constants were not only affected by the crystal phases, but also increased with the compressive strains. The stress varied with the Ba/Sr ratio, and affected the magnetoelectric properties. While Sr-addition was increased, the stress reduced, and the discontinuous change of magnetization at ferroelectric Curie temperature decreased. In NiFe2O4(NFO)/(BaTiO3)(BTO) system with different thickness of magnetic layer, the magnetoelectric coupling effect decreased with the increase of magnetic thickness. The variation of magnetization ∆M~0.16 emu/cm3 is observed in the NFO(60 nm)/BTO film near the ferroelectric Curie temperature. In contrast, due to the large interface effect, ∆M~25.46 emu/cm3 is obtained in the NFO(10 nm)/BTO bilayers. This phenomenon indicated that stress and interface effect played major roles in magnetoelectric coupling.

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