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

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Outline

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) High transparency (>80%)(band gap=3.5eV) High conductivity ( ) 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 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

Wavelength(nm)

300 350 400 450 500 550 600 650

Transmission(%)

0

20

40

60

80

100

100c150c200c250c300cZnO

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

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 met

al and rare earth elements. Exotic ferromagnetism: no magnetic ions doped fer

romagnetism. e.g. ZnO:N

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Ferromagnetic mechanisms:e.g. Spin wave excitation (RKKY); Coulomb excitation

(Stoner); Double-exchange; BMP….. BMP (bound magnetic polaron) model

Possible ferromagnetic mechanism of ZnO:N

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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22We expect the ferromagnetism of ZnO:N actually exists in an optimal N concentration

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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.