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作者(中文):吉宗驥
作者(外文):Chi, Chong-Chi
論文名稱(中文):gamma-Fe2O3/CoO core/shell奈米粒子磁性質與介面微結構關係之探討
論文名稱(外文):Investigation of relations between the interface microstructures and the magnetism of gamma-Fe2O3/CoO core/shell nanoparticles
指導教授(中文):歐陽浩
指導教授(外文):Ouyang, H.
口試委員(中文):林克偉
張晃暐
口試委員(外文):K.-W. Lin
H-W Chang
學位類別:碩士
校院名稱:國立清華大學
系所名稱:材料科學工程學系
學號:101031596
出版年(民國):103
畢業學年度:102
語文別:中文
論文頁數:156
中文關鍵詞:磁性奈米粒子介面混合
外文關鍵詞:magnetic nanoparticleinterfacial intermixinggamma Fe2O3CoO
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加拿大J. van Lierop教授團隊以無水化學合成法製備出磁性core/shell -Fe2O3/CoO奈米粒子後,使用SQUID和Mössbauer光譜測量磁性質。由SQUID發現有接shell的奈米粒子會產生交換偏壓現象,且矯頑場也會變大。而觀察Mössbauer光譜則是發現core/shell奈米粒子對抗熱擾動的能力變得非常強,加拿大J. van Lierop教授團隊臆測主要原因為core/shell介面的intermixing造成。
所以本實驗主要是使用電子顯微鏡和EDS來觀察分析奈米粒子core/shell介面。EDS顯示在介面處主要是Co滲入-Fe2O3八面體空位的行為而不是鐵滲入CoO。分析HRTEM影像可以發現-Fe2O3在core/shell邊界處有Co滲入,且Co滲入會導致材料繞射點訊號改變。用此當作依據來判斷擴散深度並分析兩種製程溫度(150°C和235°C)對擴散深度的影響。發現當製備溫度150°C時Co的平均擴散深度為0.47nm。若製備溫度升高到235°C則Co的平均擴散深度為0.67nm。
使用VASP第一原理計算對Co擴散到不同位置做能量計算,得到Co擴散到-Fe2O3八面體空位能量最低代表最可能的情況。接著我們建立出模擬結構模擬intermixing行為並使用VASP第一原理計算來探討intermixing對磁性質的影響。我們發現Co擴散到-Fe2O3八面體空位會使整體磁化量變高,使材料更偏向鐵磁性。同時也發現Co擴散深度會影響磁化量,擴散深度深磁化量反而會下降,和 J. van Lierop教授觀測到的結果相符。
又在core/shell介面因為有氧離子存在,所以我們也建立了模擬結構來探討超交換性行為對磁性質的影響。
Prof. J. van Lierop et al and we have showed that the magnetism of core-shell nanoparticles (made of maghemite, -Fe2O3, cores and transition-metal and metal-oxide shells) is altered substantially by the interface, which is a doped iron-oxide layer formed naturally during the seed-mediated synthesis process, a route used typically to produce core-shell nanoparticles. Characteristics fundamental to useful applications, such as the anisotropy and superparamagnetic blocking temperature, were altered substantially with Cu, CoO, MnO, and NiO shells. To ascertain the origin of this behavior, the prototype -Fe2O3/CoO core-shell nanoparticles are described in detail. The magnetism originates essentially from an interfacial doped iron-oxide layer formed via migration of shell ions,e.g., Co2+, into octahedral site vacancies in the surface layers of the γ -Fe2O3 core. For this system, an overall Fe
morb/mspin = 0.15 ± 0.03 is measured (morb ∼ 0 for the Fe-oxides) and an enhanced Co morb/mspin = 0.65 ± 0.03 elucidates the origin of the unexpectedly high overall anisotropy of the nanoparticle. This interfacial layer isresponsible for the overall (e.g., bulk) magnetism and provides a perspective on how the magnetism of core-shell
nanoparticles manifests from the selected core and shell materials.

Within this work, TEM and first-principles calculations to prove the core/shell intermixing and magnetic property were performed in our group. By analyzing the HRTEM and EDS, the intermixing was confirmed, mainly by the doping of Co into the octahedral site vacancies of -Fe2O3. The average Co doping depths in different processing temperatures (150°C and 235°C) were 0.47nm and 0.67nm, respectively. The error of this measurement is within 5 percent through a simulation.

By first-principles calculations, the intermixing phase of -Fe2O3 with Co doping is ferromagnetic, with even higher magnetization as compared to that of pure -Fe2O3. Besides, Co doping (same numbers) into different octahedral sites can cause different magnetizations.
總目錄
致謝…………………………………………………………………………………….I
摘要…………………………………………………………………………………...II
Abstract………………………………………………………………………………III
符號定義……………………………………………………………………………..IV
總目錄………………………………………………………………………………...V
圖目錄…………………………………………………………………………...…VIII
表目錄………………………………………………………………………...……XIII
第一章 緒論…………………………………………………………………………1
1.1前言 ……………………………………………………………………………..1
1.2研究動機 ………………………………………………………………………..5
第一章參考文獻 ……………………………………………………………………6
第二章 理論與背景 …………………………………………………………………7
2.1磁性材料基本介紹 ……………………………………………………………..7
2.1.1鐵磁性物質…………………………………………………………………...7
2.1.2順磁性物質…………………………………………………………………...8
2.1.3反鐵磁性物質………………………………………………………………...9
2.1.4反磁性物質………………………………………………………………….10
2.1.5亞鐵磁性物質……………………………………………………………….10
2.2磁異向性(magnetic anisotropy) 和交換偏壓………………………………….11
2.2.1磁晶異向性(Magnetocrystalline anisotropy)………………………………..11
2.2.2形狀異向性(Shape anisotropy)……………………………………………...13
2.2.3磁彈性異向性(Magnetoelastic anisotropy)…………………………………14
2.2.4引導磁異向性(Induced magnetic anisotropy)………………………………15
2.2.5垂直異向性………………………………………………………………….16
2.2.6交換偏壓…………………………………………………………………….17
三、Core/shell magnetic nanoparticle……………………………………………….18
3.1Core鐵磁層厚度………………………………………………………………..20
3.2Shell反鐵磁層厚度……………………………………………………………..21
3.3交換耦合J …………………………………………………………….………..23
3.4溫度…………………………………………………………………….……….24
3.5粒子尺寸…………………………………………………………….………….25
3.6FM/AFM 介面Spin同方向個數/spin反方向個數比例……………….……..26
3.7介面intermixing ………………………………………………………….……30
3.8極大的應變……………………………………………………………….…….32
四、超交換作用………………………………………………………………….….35
五、multislice原理………………………………………………………………….41
六、VASP第一原理計算……………………………………………………………48
6.1第一原理計算簡介……………………………………………………………..48
6.1.1平面波(plane wave) 與虛位勢(Pseudopotential Method) …………………49
6.1.2Muffin-Tin、Linear Muffin-Tin Method…………………………………….49
6.1.3原子軌道方法-緊密束縛近似(Tight-Binding approximation)……………..49
6.1.4第一原理計算應用…………………………………………………….……50
6.2VASP (Vienna Ab-initio Simulation Package)原理………..……………………53
6.2.1第一原理基本理論--Hartree equation………………………………………53
6.2.2第一原理基本理論--Hartree-Fock equation………………………………...56
6.2.3第一原理基本理論--密度泛函理論 (density function theorem, DFT)……56
6.2.4第一原理基本理論--局部密度近似(Local Density Functional Approximation, LDA)..58
6.2.5第一原理基本理論--廣義梯度近似(Generalized Gradient Approximation,GGA)……62
6.2.6自洽方法 (self-consist scheme)……………………………………………..65
6.2.7相對論效應影響磁晶異向性能計算……………………………………….67
6.2.8鬆弛計算的收斂準則………………………………………….……………67
七、SQUID原理……………………………………………………………………67
八、奈米粒子制備……………………………………………….…………………70
九、ABSF……………………………………………………………………………71
十、Mössbauer光譜……………………………………………..…………………78
第二章參考文獻……………………………………………………………………89
第三章 實驗方法……………………………………………………………………92
3.1實驗步驟…………………………………………………………………..……92
3.2制備奈米粒子……………………………………………….……………….…92
3.3奈米粒子電子顯微鏡試片製備……………………………….….……………93
3.1場發射穿透式電子顯微鏡………………………………………..……………94
3.5 multislice……………………………………………..…………………………95
3.6 VASP模擬計算……………………………………………………………..…100
第三章參考文獻……………………………………………………………..……102
第四章 結果與討論……………………………………………………………..…103
4.1分析製成溫度150度C的奈米粒子……………………………………...…107
4.2高倍EDS分析………………………………………………………...…...…115
4.3奈米粒子HRTEM影像:Co擴散深度分析……………..…………………116
4.4改變製程溫度的影響…………………………………………………………125
4.5準確度分析……………………………………………………………………126
4.6估算擴散深度…………………………………………………………………131
4.7VASP分析…………………………………………………………………...…132
第四章參考文獻………………………………………………………….……….140
第五章 結論……………………………………………………………………..…141
附錄…………………………………………………………………………………142
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