新穎異質磊晶鈷鐵氧可撓式高磁致伸縮效應之透明鐵磁薄膜之研發

Abstract

本研究欲研發新穎的磊晶鈷鐵氧可撓式高磁致伸縮效應之透明鐵磁薄膜，吾人將研究主要分為兩部分，其一為透明磊晶鈷鐵氧(CoFe2O4, CFO)-鈦酸鍶(SrTiO3, STO)鐵磁體異質接面系統，其二為具高磁致伸縮效應的磊晶異質鈷鐵氧可撓式系統，此研究皆透過脈衝雷射沉積法製備樣品。以X光繞射分析證實CFO-STO的磊晶關係，CFO[100]||STO[100]、CFO[010]||STO[010]與CTO[001]||STO[001]，原子力顯微鏡與穿透電子顯微鏡的結果呈現兩種材料互相纏繞的結構特徵，稱其為體異質接面系統，展現CFO奈米晶體與於STO材料進行結構耦合，超導量子干涉儀量進行磁性分析，顯示結構耦合所產生的應變現象能夠主導磁性與異向性，能夠藉由改變CFO奈米晶體與STO的組成比例達成調控。而吸收光譜與X光辭圓偏振光譜進一步支持整個體異質接面系統能夠不需犧牲太多的磁化強度，就能達成高光穿透率的目標，此項研究不僅提供一個透明且帶有鐵磁性的磁鐵無須在透光度與磁化強度間做取捨而製備出來。另外也成功製備一種由可撓式白雲母基板與異質磊晶CFO膜所組成的新穎磁致伸縮雙層樣品系統，藉由反射式高能電子繞射儀發現CFO膜遵循逐層的成長模式，以X光繞射分析證實CFO與Mica的磊晶關係，CFO[111]||Mica[001]、CFO[1-10]||Mica[010]與CFO[-1-12]||Mica[100]，SQUID儀器中和靜磁力顯微鏡中分析結果呈現CFO/Mica異質結構的樣品具有抵抗形變的強韌磁性，另外數位全像顯微鏡演示可透過磁力控制CFO/Mica異質結構的樣品形變能力與計算此樣品具有極大的磁致伸縮表現。最後將前兩部分的研究合併在一起，發現確實能夠在Mica上成長由CFO與STO組合成複合材料系統，然而欲透過STO基板上的製程轉移至可撓的Mica時，雖磁性表現與第二部分的實驗雷同，但無法展現良好的透光特性，而我們期許利用複合材料系統概念製備一個新穎可撓透明鐵磁薄膜。

In this study, we expect to develop an novel flexible, ferromagnetic and transparent thin film with large magnetostrictive effect composed of heteroepitaxial CoFe2O4. The study is mainly separated into two parts. One is transparent epitaxial CoFe2O4-SrTiO3 bulk heterojunction system, and the other one is flexible thin film with large magnetostrictive effect composed of heteroepitaxy CoFe2O4. Samples were fabricated through pulsed laser deposition method in this study. The epitaxial relationships, CFO[100]||STO[100], CFO[010]||STO[010] and CTO[001]||STO[001], between CFO and STO are confirmed by x-ray diffraction analysis. Atomic force microscopy and transmission electron microscopy images show CFO and STO entangling together, and this kind of system is called bulk heterojunction system. Superconductive quantum interference device is conducted to measure magnetic properties. The magnetization and magnetic anisotropy are dominated by the strain, which can be tuned by the composition ratio of CFO and STO. The transmission spectrum and x-ray magnetic circular dichroism further prove that it doesn’t need to sacrifice too much magnetization to achieve high transmission in the bulk heterojunction system. In another part of study, layer-by-layer growing mode in CFO film is discovered by reflection high energy electron diffraction. The epitaxial relationships, CFO[111]||Mica[001], CFO[11 ̅0]||Mica[010] and CFO[(11) ̅2]||Mica[100], between CFO and Mica are confirmed by x-ray diffraction analysis. CFO/Mica bimorph has solid magnetism to resist the deformation from SQUID and magnetic force microscopy analysis. Digital holographic microscopy shows that we can deform CFO/Mica bimorph by appling external magnetic field, and also determine high magnetostrictive behavior in this system. Then we combine these two parts of study. CFO and STO nanocomposite system can successfully fabricated on muscovite substrate. Although the magnetic behavior is similar to the second part, this system can’t exhibit excellent transmission. We expect to fabricate a novel transparent flexible magnetic film via the nanocomsite system.