Transcript 演講投影片 - 國立中興大學物理學系

Possible ferromagnetic mechanism
in non-magnetic ion doped transition
metal oxides
孫士傑
國立高雄大學 應用物理系
2012/5/11 中興大學物理系
Outline
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Introduction and Motivation
Model and Theory
Results and Discussion
Summary
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Introduction and Motivation
 Transparent Conducting Oxides (TCO)
在現今的先進世界，透明導電溥膜 (ITO) 被廣泛應用在高級的電子產品上。
例如：電子手機、觸控式顯示屏和開關等…………
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Indium Tin Oxide (ITO)
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High transparency (>80%)(band gap=3.5eV)
High conductivity (
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High stability
High cost
Very few in our Earth
N-type almost
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Transparency vs. Conductivity
 在可見光波長範圍內具有可接受之透光度
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 導電度增加，透明度減少(電漿效應)
 可接受的條件: 透明度80%,電阻率
TCO在短波長透光範圍：由隙的能(energy gap)決定
在長波長透光範圍：由電漿頻率的決定
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Requirement for Replaced materials
 Large Band Gap
 Direct band
 Good conducting
Transmission(%)
100
80
60
100c
150c
200c
250c
300c
ZnO
40
20
0
300
350
400
450
500
550
Wavelength(nm)
600
650
ZnO
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取代ITO的TCO
各種TCO材料- ZnO系透明導電膜(band gap = 3.4 eV)
 ZnO (3~5 ×10-4 Ω-cm)
 ZnO:In (IZO) (2~4 ×10-4 Ω-cm , 脈衝雷射沉積法)、
 ZnO:Ga(GZO) (1.2×10-4 Ω-cm, 減壓MOCVD 法)、
 ZnO:Al (AZO) (1.3×10-4 Ω-cm, 脈衝雷射沉積法)、
 ZnO:Ti
特點：
 1. ZnO取得容易
 2. 價格比便宜
 3. 製控制容易
 3. 穩定性比ITO 差
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Other comparable materials
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ZnO applications
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太陽電池
顯示器透明電極
觸控面板
體聲波元件
壓電基板
防電磁波干擾屏蔽
熱輻射屏蔽(Low-E)
抗靜電膜
除霧發熱膜….等
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Spintronics(自旋電子元件)
 Charge + Spin multi-functions
 DRAM
MRAM
 Small band gap magnetic semiconductors:
III-V GaAs:Mn (< 150K)
 Large band gap magnetic semiconductors:
III-V GaN:Mn (>300k), ZnO:Co (>400k)
 ZnO: Good candidate for Spintronics.
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Magnetism
Quantum correlated effect
Para- Ferro- and Anti-ferromagnetism
Arise from L (angular momentum) or S (spin)
Most observed in incompletely filled transition
metal and rare earth elements.
 Exotic ferromagnetism: no magnetic ions
doped ferromagnetism. e.g. ZnO:N
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Possible ferromagnetic mechanism
of ZnO:N
 Ferromagnetic mechanisms:
e.g. Spin wave excitation (RKKY); Coulomb
excitation (Stoner); Double-exchange; BMP…..
 BMP (bound magnetic polaron) model
Oxygen vacancies: carriers
capturing centers
From J. D. M. Coey
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Defect induced magnetism
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Theory and model
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=
+
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Results and Discussions
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We expect the ferromagnetism of ZnO:N actually exists in an optimal N concentration
Summary
 We propose a ferromagnetic model to investigate how the ferromagnetism
possibly exists in non-magnetic ion doped transition metal oxides.
 Our studied sample is the nitrogen embedded ZnO, ZnO:N, which has been
confirmed by the experiments that the robust ferromagnetism exactly exists in
room temperature.
 We propose the ferromagnetism in ZnO:N to be induced from the Coulomb
excitation taking place in the localized VO band.
 The ferromagnetism prefer appearing in deep donor VO states rather than in
shallow states.
 The electron-phonon coupling suppresses the ferromagnetism from the deep
donor states yet enhances the ferromagnetism from the shallow donor states.
 Low phonon energy prefers driving the deep donor states to induce the
ferromagnetism.
 The increase of the coupling between VO states and OZN narrow band prefers
inducing the ferromagnetism from deep donor states.
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