氧化殼層對於錫奈米顆粒超導性與自旋極化的影響; Effects of oxide shell on superconductivity and spin polarization in Sn nanoparticles

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题名:	氧化殼層對於錫奈米顆粒超導性與自旋極化的影響;Effects of oxide shell on superconductivity and spin polarization in Sn nanoparticles
作者:	李其紘;Chi-Hung Lee
贡献者:	物理研究所
关键词:	奈米顆粒;超導;自旋極化;superconductivity;nanoparticles;spin polarization
日期:	2010-07-20
上传时间:	2010-12-08 14:23:32 (UTC+8)
出版者:	國立中央大學
摘要:	本論文中藉由改變錫奈米顆粒表面氧化殼層厚度來探討奈米顆粒的超導性以及磁性。本實驗使用熱蒸鍍法製備6 nm錫顆粒，再利用加熱氧化來製備具有核殼結構的Sn/SnO奈米顆粒，以固定的溫度不同的加熱時間來控制氧化程度，並且使用X光繞射來分析樣品的成分及粒徑，再從成分比例來計算殼層的厚度。為了探討錫奈米顆粒的超導性，我們進行一系列的磁化率量測，並用磁化率隨溫度的變化關係藉由Scalapino表示式擬合判定超導參數。我們觀察到超導相變溫度隨著氧化後核心變小而先增後減。由磁化強度隨外加磁場的變化量測，我們在低外加磁場觀察到自旋極化，以及在高外加磁場觀察到冷次反磁(Lentz diamagnetic)，並使用朗之萬(Langevin function)以及冷次反磁項來描述磁矩隨外加磁場改變行為，而能觀察到磁矩隨著氧化殼層先減後增的情形。並推測超導溫度升高是因為自旋極化效應減小所致。 Sn nanoparticles are fabricated by employing thermal evaporation method and subsequently oxidized in air at a temperature under various oxidation times. XRD is utilized to determine the mean particle diameter (6 nm) of the Sn nanoparticles as grown. The composition of Sn/SnO is analyzed by refining the X-ray diffraction pattern using General Structural Analysis System (GSAS) program. The core diameter is calculated from the composition. In our study, the superconducting diamagnetic screening effect was measured through AC magnetic susceptibility (χac=χ’ +iχ’’). The temperature dependence of in-phase component χ’(T) can be described by the Scalapino’s expression, which allows to extract the superconducting transition temperature. The spin polarization effects are seen in M(H) curve which can be described by Langevin function, revealing the coexistence of superconductivity and spin polarization. As the core diameter getting smaller, we found the interplay between the superconducting transition temperature and the spin polarization.
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