銅氧核殼奈米顆粒間交互作用對自旋極化之影響

Effects of interparticle interaction on spin-polarized Cu/O core-shell nanoparticles

陳乃維(Nai-Wei Chen)

指導教授 ： 李文献

國立中央大學/理學院/物理學系/碩士(2008年)

摘要

使用低真空熱蒸鍍冷凝製程獲得樣品Cu0518，透過結構精算軟體分析的X光繞射圖、EDS及XRF得到成分為銅及氧組成，帶有極少的鎢，成分比Cu 69.2%、Cu2O 30.8%。使用共同體積函數及積分寬法分析X光繞射圖與SEM影像統計定義樣品粒徑，配合成份比例得到核心粒徑 13.7nm、殼層厚度2.4 nm的銅氧核殼奈米顆粒。
使用本實驗室物理特性量測系統對Cu/Cu2O奈米顆粒做磁性量測，觀察到抗磁性及兩個磁分量三者共存的磁特性，兩磁分量分別為核心銅及殼層氧化亞銅的自旋極化現象，於55K附近存在特異磁性，在變溫磁化強度量測上出現隨溫度變化的峰形，於峰形存在的溫度區間，磁化曲線觀察到與反鐵磁性物質類似的峰腰型磁滯。而核心銅的磁分量在磁場1T便達飽和，殼層氧化亞銅的磁分量則須更高磁場才達飽和，並在溫度高於40K之後便消失。
進一步透過壓合樣品調控顆粒間距，觀察奈米顆粒間的交互作用。發現兩個磁分量在間距小於5 nm受到磁偶矩-磁偶矩交互作用影響而飽和磁化強度減少，而特異磁性存於變溫磁化強度的峰形在核心間距小於5 nm時明顯轉弱。而Cu/Cu2O奈米顆粒的抗磁性受交互作用影響，呈現隨顆粒間距三次方增加關係。

關鍵字

核殼 ； 銅 ； 奈米顆粒 ； 自旋極化 ； 交互作用

並列摘要

The sample Cu0518 was fabricated by the thermal evaporation method. EDS, XRF, SEM and XRD patterns were used to characterize the sample. The analysis show that the Cu/Cu2O mole ratio are 7/3, with a 13.7 nm Cu core and a 2.4 nm Cu2O shell.
The magnetic properties of Cu/Cu2O nanoparticle was investigated by magnetization and ac magnetic susceptibility measurements. Two magnetic components and a diamagnetic one were observed, which were attributed to the spin polarization of Cu core, spin polarization of Cu2O shell, and diamagnetic responses. Hysteresis loop in M(H) and an anomaly in M(T) were found at around 55K. The analysis of M-H curve show that the Cu component saturated at 1T while the Cu2O component requires a higher applied magnetic field for saturation. No contribution from Cu2O was found above 40K.
Interparticle interaction becomes dominated when the average particle separation is smaller than 5 nm, which result in a reduction in saturation magnetization. The relation between average particle separation and diamagnetism can be described by the cubic law.

並列關鍵字

nanoparticle ； spin polarization ； core shell ； interaction

參考文獻

[1] Charles Kittel, Introduction to Solid State Physics ( eighth edition )

[4] 吳勝允、李文獻，奈米銀微粒的非線性磁激發，物理雙月刊28卷五期 p.820 (2006)

[8] 王進威，擬合X光繞射峰形判定奈米微粒粉末的粒徑分佈，中央大學碩士論文(2006)

[9] 陳書偉，粒子間交互作用對奈米錫自旋極化的增益效應，中央大學碩士論文(2007)

[13] V. Sahni and K.-P. Bohnen, “Exchange charge density at metallic surfaces,” Phys. Rev. B 29, 1045 (1984)