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系統識別號 U0026-3101201810205700
論文名稱(中文) Tb2Ir2O7 之磁性研究
論文名稱(英文) Magnetic Properties of Tb2Ir2O7
校院名稱 成功大學
系所名稱(中) 物理學系
系所名稱(英) Department of Physics
學年度 106
學期 1
出版年 107
研究生(中文) 簡冠程
研究生(英文) Kuan-Cheng Chien
學號 L26054035
學位類別 碩士
語文別 英文
論文頁數 93頁
口試委員 指導教授-張烈錚
口試委員-呂欽山
口試委員-王立民
中文關鍵字 銥燒綠石化合物  Tb2Ir2O7  電阻  磁化率  比熱  µSR  中子散射  磁結構  自旋波 
英文關鍵字 iridated-pyrochlore  Tb2Ir2O7  resistivity  magnetization  specific heat  µSR  neutron scattering  magnetic structure and spin wave 
學科別分類
中文摘要 近年來有大量的研究深入探討銥燒綠石化合物(iridated-pyrochlore)其獨特的物理現象,因其具備5d電子軌域而產生電子與電子關聯和自旋軌道耦合交互作用,在本文中我們利用固態合成法燒製樣品Tb2Ir2O7並探討多項實驗結果顯示的物理性質,從電阻、磁化率與µSR量測中驗證其在132K特有的導體絕緣體相變(metal-insulator transition),並且同時在磁化率與µSR實驗同時觀察到在50 K和6 K的磁相變符合Tb-Ir與Tb-Tb交互作用造成的磁排列變化。歸納各項實驗數據得出Tb3+在50 K下受長程有序排列的Ir4+影響,在低溫下也形成反鐵磁性全進全出(all-in-all-out)形式的磁結構。我們在比熱數據中新發現0.1 K處出現明顯尖峰,且此訊號符合肖特基(Schottky)效應,進一步分析此比熱來源為Tb3+原子核內部的電磁場所產生的超精細結構所造成。從低溫下Tb3+磁性貢獻熵的計算上得到數值接近於Rln4,並藉由非彈性中子散射實驗確認Tb3+在基態和第一激發態為二重態。我們提出可能的交互作用力建構此系統的自旋波(spin wave)模型,並且驗證Tb3+強烈的最近鄰交互作用貢獻造成反鐵磁性全進全出有序排列磁結構。
英文摘要 In recent years, iridated-pyrochlore compounds with 5d-electron elements have attracted a lot of interest primarily because of the electron-electron correlations and spin-orbit interactions in these materials. We have prepared polycrystalline samples of pyrochlore Tb2Ir2O7 using conventional solid state reaction and we will present results from XRD, resistivity, magnetization, specific heat, µSR and neutron scattering experiments. Three anomalies at T ~ 132 K, 50 K and 6 K have been observed in our DC magnetization measurements. Our magnetization and resistivity measurements on Tb2Ir2O7 confirm that Ir4+ ions are ordered and undergo a metal-insulator transition (MIT) at TMI ~132 K. The muon spin relaxation (μSR) results reveal internal static field below the metal-insulator transition temperature (TMI), and three anomalies in the μSR oscillation frequencies observed near 130 K, 50 K and 6 K are consistent with the results of DC magnetization. The magnetic structure of Tb2Ir2O7 below 50 K is an antiferromagnetic "all-in-all-out" (AIAO) state. The new observed sharp peak revealed at ~0.1 K in specific heat is in line with the form of the Schottky specific heat of the Tb3+ nuclear hyperfine. The time-of-flight inelastic neutron scattering results and spin wave calculation confirm the integrated magnetic entropy approaches to the value of Rln4, indicating a doublet-doublet scheme for Tb3+ in the system. We propose the spin wave excitation model from a candidate exchange interactions, we found the strong nearest-neighbor antiferromagnetism AIAO ordered by Tb3+ sublattice.
論文目次 摘要 I
Abstract II
Acknowledgments IV
List of Table IX
List of Figures X
Chapter.1 Introduction 1
1.1 Pyrochlore Oxide 2
1.2 Ir- Pyrochlore Oxide 5
1.3 Scope of this thesis 11
Chapter.2 In-house Experimental Methods 12
2.1 Sample Preparation 13
2.2 SQUID VSM 14
2.2.1 DC Magnetization 15
2.3 PPMS 17
2.3.1 Heat capacity 20
2.3.2 Resistivity 21
2.3.3 AC susceptibility 22
2.4 X-ray Powder Diffraction 24
Chapter.3 Synchrotron radiation X-ray 25
3.1 X-ray diffraction 25
3.2 BL01-C2, TLS, NSRRC 27
3.3 Experimental method 29
Chapter.4 Neutron Scattering 30
4.1 Neutron diffraction 32
4.1.1 ECHIDNA 34
4.2 Inelastic neutron scattering 35
4.2.1 PELICAN 36
4.2.2 Experimental method 37
Chapter.5 μSR 39
5.1 Muon 40
5.2 µSR technique 42
5.3 µSR facilities 44
5.4 GPS instrument, PSI 47
5.5 Experimental method 50
Chapter.6 Result and discussion 51
6.1 XRD and structure 51
6.2 Resistivity 55
6.3 Magnetometry 55
6.4 Heat capacity 59
6.5 μSR 62
6.6 Neutron powder diffraction 69
6.7 Inelastic Neutron scattering 74
Chapter.7 Conclusion 79
Chapter.8 Future work 81
Appendix 82
A. Ir-227 single crystals synthesis 82
B. SpinW 84
Bibliography 88

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