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論文名稱 Title |
含有空缺及鎵的雜質的參雜鈷氧化鋅內鐵磁及反鐵磁耦合的相互競爭 Competition between ferromagnetic and anti-ferromagnetic couplings in Co doped ZnO with vacancies and Ga co-dopants |
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系所名稱 Department |
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畢業學年期 Year, semester |
語文別 Language |
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學位類別 Degree |
頁數 Number of pages |
57 |
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研究生 Author |
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指導教授 Advisor |
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召集委員 Convenor |
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口試委員 Advisory Committee |
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口試日期 Date of Exam |
2012-01-16 |
繳交日期 Date of Submission |
2012-02-14 |
關鍵字 Keywords |
鐵磁性、反鐵磁性、氧空缺、鋅空缺、磁性性質、氧化鋅 Zn vacancies, O vacancies, antiferromgnetism, magnetic properties, ferromagnetism, ZnO |
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統計 Statistics |
本論文已被瀏覽 5662 次,被下載 488 次 The thesis/dissertation has been browsed 5662 times, has been downloaded 488 times. |
中文摘要 |
本研究使用自旋極化的第一原理方法計算參雜鈷之氧化鋅(含鈷氧化鋅)之電子結構及系統總能以了解含有空缺及共同參雜鎵對於含鈷氧化鋅之磁性性質的影響。本研究顯示在順磁態,即鈷原子沒有磁矩,的情況下,含鈷氧化鋅的總能過高而且不穩定。由系統總能的計算結果也發現,含有鋅空缺及共同參雜鎵的含鈷氧化鋅其穩定態分別為反鐵磁態及鐵磁態,而含有氧空缺的含鈷氧化鋅其穩定態為弱鐵磁態。這些磁性特性可經由含有氧、鋅空缺及共同參雜鎵所產生的含鈷氧化鋅之電子結構的變化來了解,由這些變化知道鈷原子之間的反鐵磁偶合是藉由在價帶中氧的2p及鈷的自旋向上3d軌道的混成軌域所媒介;而鈷原子之間的鐵磁偶合為在氧化鋅的能隙中源自氧空缺的p狀態或是鎵的sp狀態所媒介。對於含有鋅空缺的含鈷氧化鋅,反鐵磁偶合較鐵磁偶合強而呈現反鐵磁態;對共同參雜鎵的含鈷氧化鋅而言剛好相反,而呈現鐵磁態;至於含氧空缺的含鈷氧化鋅,反鐵磁及鐵磁偶合增強的程度相當,而呈現弱鐵磁態。此研究顯示在含有氧、鋅空缺及共同參雜鎵的含鈷氧化鋅中有鐵磁偶合及反鐵磁偶合的競爭,它們之間的微細平衡決定這些材料的磁性特性。 |
Abstract |
Spin-polarized first-principles electronic structure and total energy calculations have been performed to better understand the magnetic properties of Co doped ZnO (ZnO:Co) with vacancies and Ga co-dopants. The paramagnetic state of ZnO:Co, in which Co ions lose their magnetic moments, has been found to be unstable. The total energy results show that acceptor-like Zn vacancies and donor-like Ga co-dopants render the anti-ferromagnetic (AFM) and ferromagnetic (FM) states to be more favorable, respectively. With O vacancies, ZnO:Co has been found to be in the weak FM state. These magnetic properties can be understood by the calculated O- and Zn-vacancies and Ga-co-dopant induced changes of the electronic structure, which suggest that AFM and FM Co-Co couplings are mediated by O 2p-Co majority (↑)-spin 3d hybridized states in the valence band of ZnO and O-vacancy-derived p states or Ga sp states in the ZnO band gap, respectively. For ZnO:Co with Zn vacancies (Ga co-dopants) the AFM (FM) coupling outweighs the FM (AFM) coupling and results in the AFM (FM) state, while for ZnO:Co with O vacancies, both the FM and AFM couplings are enhanced by similar degrees and result in the weak FM state. This study reveals a competition between FM and AFM couplings in ZnO:Co with vacancies and Ga co-dopants, the detailed balancing between which determines the magnetic properties of these materials. |
目次 Table of Contents |
論文審定書………………………………………..……...…..i 致謝………………………………………………..…...…….ii 摘要………………………………………………..…...……iii Abstract………………………………………....………......iv I. Introduction ...………………....………………………….1 II. Theory…………………....…………………………...…..4 2-1 The density functional theory (DFT) with the local-density approximation (LDA)…...………..4 2-2 The pseudofunction (PSF) calculation method.…11 III. Structural models and calculation details….……...20 IV. Results and Discussion………………………………….......………...24 V. Conclusion………………...…………………………...30 References………………………………......…...……….32 Tables……..………………………………………………37 Figures Captions………………………………………………......38 |
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