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博碩士論文 etd-0521116-140846 詳細資訊
Title page for etd-0521116-140846
論文名稱
Title
自旋頓挫系統Cu2OCl2之多鐵性研究
Multiferroics in spin frustrated system Cu2OCl2
系所名稱
Department
畢業學年期
Year, semester
語文別
Language
學位類別
Degree
頁數
Number of pages
77
研究生
Author
指導教授
Advisor
召集委員
Convenor
口試委員
Advisory Committee
口試日期
Date of Exam
2016-06-19
繳交日期
Date of Submission
2016-06-27
關鍵字
Keywords
反鐵磁性、焦綠石結構、Cu2OCl2、幾何自旋頓挫系統、鐵電性、多鐵性
multiferroic, ferroelectricity, antiferromagnetism, pyrochlore lattice, Cu2OCl2, spin frustrated system
統計
Statistics
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The thesis/dissertation has been browsed 5690 times, has been downloaded 809 times.
中文摘要
幾何自旋頓挫態系統具有很特別的物理特性,此系統在基態時能量最低,但在某些幾何晶格中,自旋為了滿足能量最低的基態條件卻無法呈現一個規則且特定的方向。這些晶格包含三角晶格、籠紋晶格、焦綠石晶格以及尖晶石結構。
本篇研究的樣品Cu2OCl2的晶格結構為焦綠石結構,焦綠石結構是由數個共角四面體組合而成,也因為其幾何不穩定性加強了電子的關聯性以及量子效應。藉由磁性量測及比熱實驗證實此材料為涅爾溫度70 K的反鐵磁性物質。而我們主要研究的是此材料的電性,以及討論造成此性質的原因。
電性量測方面,從介電係數實驗得知Cu2OCl2在75 K附近存在一個明顯的轉折。在轉折溫度之上與之下各取一個溫度點進行磁電實驗並發現在此溫度之下具有磁電效應。藉由pyroelectric current實驗證實此材料在75 K以下會產生自發極化現象。這些實驗證明此材料具有鐵電特性。
我們利用可變溫的X光繞射儀探討在不同溫度下結構的變化。結果指出,隨著溫度的下降,晶格常數a與c會逐漸變小,而晶格常數b則有變大的趨勢。材料的晶格體積則在75 K附近的溫區有顯著的變化,證明此材料結構的改變會引發鐵電特性。最後,我們利用DM交互作用來解釋Cu2OCl2的多鐵性,這個研究結果使我們了解高溫多鐵材料的特性並協助開發新的高溫多鐵材料。
Abstract
Geometrical spin frustrated system shows special and interesting physical properties. The energy of this system will be lowest in the ground state. Nevertheless, the spin ordering in some geometric lattices cannot stay in the particular direction in order to meet minimum energy in the ground state such as triangular lattice, Kagome lattice, Pyrochlore lattice and spinel structure.
Cu2OCl2 attracts much attention due to its pyrochlore lattice which has the corner-sharing tetrahedral and the geometrical frustration, leading to strong electron correlation amd quantum effect. The experimental results, including the magnetic properties and specific heat, confirmed that Cu2OCl2 is antiferromagnetism and has Néel temperature ~70K. Our research focused on the electrical properties of this material, and discussed the reasons of these phenomena.
Ferroelectric ordering is determined by using dielectric constant and electric polarization and the TC of the material ~75 K. The structural distortion observed by the temperature dependence of lattice constants (volume) is considered as the role to induce ferroelectricity. The mechanism of multiferroic in Cu2OCl2 might be related to the inverse DM interaction. Our findings must open a new candidate to attract more attention for the high TC multiferroic material.
目次 Table of Contents
論文審定書 i
致謝 iii
論文摘要 iv
Abstract v
目錄 vi
圖目錄 viii
第一章 簡介 1
1-1多鐵性介紹 1
1-2 Cu2OCl2 8
1-3 研究動機 11
第二章 如何製作樣品及實驗儀器介紹 12
2-1 固態合成法製備Cu2OCl2 12
2-2 X-Ray粉末繞射儀 14
2-3 磁性量測儀器 16
2-3-1 超導量子干涉磁量儀 16
2-3-2 磁性量測方法 21
2-4 電性量測儀器 24
2-4-1 封閉循環冷卻系統 24
2-4-2 電性量測方法 26
2-5 比熱原理與儀器原理[47] 29
2-5-1 比熱原理 29
2-5-2 比熱實驗儀器原理 33
第三章 實驗結果與討論 37
3-1 Cu2OCl2的X-ray繞射分析 37
3-2 Cu2OCl2磁性量測結果與討論 40
3-3 Cu2OCl2比熱量測結果與討論 44
3-4 Cu2OCl2電性量測結果與討論 45
3-5 Cu2OCl2在不同溫度下的X-ray繞射及結構分析 49
第四章 結論 57
參考文獻 59
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