載子對於摻銅氧化鋅之鐵磁有序度研究

Abstract

這篇工作主要在探討載子的作用及氧空缺(VO)的出現對摻銅氧化鋅之鐵磁有序度的影響。我們利用快速環保的反溶液法製備摻銅氧化鋅，於先前的研究中發現，其因摻雜磁矩附近有氧空缺出現破壞了對稱性且重組了自旋組態而具有局部鐵磁有序度。此篇研究將摻銅氧化鋅分別在氬氣及氧氣環境中進行快速退火，進而影響其樣品中的載子濃度，達到改變其鐵磁有序度的目的。結合同步輻射技術及Mott-Schottky分析，我們發現經氬氣處理的樣品擁有較高的載子濃度同時也含有較多的氧空缺量，而經氧氣處理的樣品則相反。在低溫的磁性量測發現氬氣及氧氣處理的樣品皆出現順磁的行為，推測其因低溫時熱電子回填至價帶使自由電子減少，在減少自由電子媒合的情況下，磁矩間偶合變弱而有順磁行為產生。但在氬氣處理的樣品中發現其相較氧氣處理的樣品有較大的磁化量及熱抗性，具有較穩定的鐵磁有序度。透過改變載子濃度工程，我們希望能更深入了解寬能隙氧化物材料中的鐵磁性以及能進一步應用在半導體自旋電子技術上。

This work aims at investigating the role played by charge carrier in relation to oxygen vacancy (Vo) in mediating the ferromagnetic order in Cu-doped ZnO nanoparticle(denoted Cu_ZnO). Synthesized by an environment-friendly anti-solvent method, Cu_ZnO exhibits localized ferromagnetic order at room temperature resulting from the broken symmetry spin (BSS) bound to dopant. We demonstrate an effective tuning of Cu_ZnO’s ferromagnetism by means of varying the carrier concentration (c.c.) via an Ar/O2-treated rapid thermal annealing process. Combining synchrotron-based spectroscopy and Mott-Schottky analyses, we found that the Ar-treatment could result in the rise of c.c. in Cu_ZnO with a simultaneous increase of the Vo concentration, while O2-treatment exerted an opposite effect on the evolution of c.c./Vo. Temperature-dependent magnetic phase characterizations revealed that both Ar-treated and O2-treated Cu_ZnO featured noticeable paramagnetism below room temperature, which signaled a lack of carrier mediation to form the ferromagnetic order. However, Ar-treated Cu_ZnO could yield a larger ferromagnetic moment as well as a higher sustainability to resist thermal fluctuation compared to O2-treated Cu_ZnO. By varying carrier concentration through Vo control, we hope to provide a better understanding to how to develop robust ferromagnetic order in wide-band-gap oxide materials in order to further advance semiconductor-based spintronics technology.