臺灣博碩士論文加值系統

鈷鐵氧體(CoFe2O4;CFO)是一種具有亞鐵磁性及磁異向性特徵的材料，並且因為磁致伸縮(magnetostriction)的特性，其在磁性感測器上的應用也被廣泛的討論，之前的文獻已顯示出CFO薄膜的磁性特徵會受到晶格形變的影響而改變。為了討論CFO與應變相關的機制，本研究中將CFO薄膜沉積在可撓式的雲母(mica)基板上，因此可藉由控制雲母基板的曲率半徑來改變施加在CFO薄膜上的應力大小，而應力會扭曲CFO的晶格。本研究中將利用拉曼光譜儀(Raman spectroscopy)量測鈷鐵氧薄膜在不同應力下聲子的振動行為，並且藉由觀察CFO A1g振動模態的頻移可以估算出其晶格常數的變化。之後利用變溫拉曼實驗觀察其振動峰半高寬在不同應力下的變化，並討論應力對CFO發生陽離子躍遷效應的影響，接著利用拉曼振動峰的頻移，觀察施加不同應力時對磁致伸縮效應的影響。最後利用磁力顯微鏡(Magnetic force microscopy;MFM)，進一步探討應力對CFO薄膜表面磁矩的影響。

Cobalt ferrite, CoFe2O4, has unique magnetic properties among other spinel ferrites such as high magnetocrystalline anisotropy constant as well as a large magnetostriction constant, which can change its magnetic properties by exert different stress on it, or will change its strain state under a different magnetic field.
The response of CoFe2O4 thin film under different strain state is studied by Raman spectroscopy. We mainly observed the shift of normal mode’s frequency under different strain, and the full width of half maximum under varies temperature with different strain state. CoFe2O4 thin film was deposited on a flexible Muscovite(mica) substrate, which we can exert a stress on CoFe2O4 thin film by curving mica substrate.
The Raman modes show an increase in frequency when increasing an in-plane compress strain. In contrast, it shows a decrease in frequency when increasing an in-plane tensile strain. And the energy that cation migration needs become fewer with increasing stress, thus we can observe cation migration effect with lower temperature.
Different strain state will distort CoFe2O4’s lattice to change the direction of CoFe2O4’s easy axis and affect it magnetic properties. Moreover, different stress on CoFe2O4 will even change it lattice volume.

摘要 I
Abstract II
誌謝 VI
目錄 VII
表目錄 X
圖目錄 X
第一章 緒論 1
第二章 磁性原理與文獻回顧 3
2.1磁性材料 3
2.1.1物質磁性簡介 3
2.1.2磁致伸縮原理 8
2.1.3 超交換交互作用 12
2.1.4 亞鐵磁性 13
2.1.5 鐵氧磁體的性質 14
2.2 文獻回顧 17
2.2.1 鈷鐵氧體基本性質 17
2.2.2 由拉曼觀察應力對晶格結構的影響 19
2.2.3 CFO陽離子躍遷效應 25
2.2.4 施加應力後對陽離子躍遷效應的影響 36
2.2.5 鈷鐵氧體磁致伸縮效應 42
第三章 實驗原理與方法 48
3.1拉曼光譜原理 48
3.1.1拉曼散射機制 48
3.1.2 拉曼散射的古典波動模型 50
3.1.3微拉曼(micro Raman)散射系統介紹 52
3.2掃描式探針顯微術(Scan Probe Microscopy) 53
3.2.1掃描式探針顯微術的工作原理 54
3.2.2原子力顯微鏡之系統架構(Atomic Force Microscopy) 55
3.2.3原子力顯微鏡成像原理 58
3.3磁力顯微鏡(MFM) 61
3.4實驗流程 65
第四章 結果與討論 68
4.1 受應力調變結構的拉曼光譜 69
4.1.1 鈷鐵氧體在雲母基板上的基本性質 69
4.1.2 鈷鐵氧體(CoFe2O4;CFO)的拉曼振動模態 72
4.1.3 計算不同曲率半徑的應力 76
4.1.4 轉偏振分析CFO薄膜在實驗室座標的晶格向量 79
4.1.5 受應力後鈷鐵氧體振動峰的變化 82
4.2受應力調變影響的陽離子躍遷效應 92
4.2.1 未施加應力的陽離子躍遷效應 92
4.2.2 施加不同應力後對陽離子躍遷的影響 95
4.3受應力調變影響的磁場中行為 114
4.3.1 在雲母片上之鈷鐵氧體薄膜的磁致伸縮現象 115
4.3.2 不同應力下的磁致伸縮現象 120
4.3.3 外加應力對CFO表面磁矩的影響 129
第五章 結論 131
參考文獻 133

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