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Possible ferromagnetic mechanism in non-magnetic ion doped transition metal oxides

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. Introduction and Motivation Model and Theory Results and Discussion Summary. Introduction and Motivation. Transparent Conducting Oxides (TCO).

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Possible ferromagnetic mechanism in non-magnetic ion doped transition metal oxides

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  1. 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

  2. Outline • Introduction and Motivation • Model and Theory • Results and Discussion • Summary

  3. 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…………

  4. 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

  5. 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

  6. Requirement for Replaced materials • Large Band Gap • Direct band • Good conducting ZnO

  7. 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

  8. Other comparable materials

  9. ZnOapplications • 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

  10. 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.

  11. 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

  12. 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

  13. Defect induced magnetism

  14. Theory and model

  15. = +

  16. Results and Discussions

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

  18. 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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