In/Ni 奈米複合材料的電子傳輸與超導性;Superconductivity and electron transport properties of In/Ni nanocomposites

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題名:	In/Ni 奈米複合材料的電子傳輸與超導性;Superconductivity and electron transport properties of In/Ni nanocomposites
作者:	王哲倫;Zhe-lun Wang
貢獻者:	物理研究所
關鍵詞:	超導;電子傳輸;奈米顆粒;跳躍式傳輸;自旋極化;自旋相關;雙分量;類二類;type Ⅱ like;two component;electron transport;nanoparticles;hopping conduction;Ferromagnetic spin polarization;spin dependent;superconductivity
日期:	2009-06-22
上傳時間:	2009-09-22 11:01:01 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文探討超導/磁性系統。透過磁化率、磁化強度與電阻率實驗，分別使用了粒徑較小(超導抗磁性較弱)的In_A 及粒徑較大(超導抗磁性較強)的In_B 混入相同的Ni 鐵磁性微粒，依序討論兩類共五組In/Ni 奈米複合材料之磁性與超導性質。鎳奈米顆粒因其磁性或顆粒間鄰近效應破壞系統超導性。此外，系統電子傳輸展現特殊雙分量行為，我們利用自由電子模型及GL 理論計算樣品Ginzburg-Landau 參數κ，根據二類超導體的指標性參數κ » 1，我們的系統歸類於類二類超導體。粒徑較大與粒徑較小樣品表現出截然不同之物理特性。且超導抗磁對應於磁化率對磁場的曲線，僅展現在粒徑較大樣品中，反之，粒徑較小樣品則否。小顆粒複合材料中，低於超導溫度後展現出超導性與跳躍式電子傳輸共存。高於超導溫度則為自旋相關磁阻，低於超導溫度由於古柏對之磁擾動使磁阻曲線有一峰值，高磁場區域為負磁阻行為。大顆粒複合材料中，In50-Ni50 除了超導抗磁相變外，低溫2.5 K 附近磁化率與磁化強度皆存在一個上揚(upturn) 為順磁性居禮 (Curi)T-1 的形式，展現出磁性分量的表徵，說明超導與鐵磁自旋極化共存。且R-T 展現出與超導有關的雙凹入式電阻行為，並認為凹入式電阻行為與自旋極化之磁分量無關。 In this thesis we report on the characteristics of nanocomposite systems that are prepared by mixing superconducting and ferromagnetic materials. The influence of magnetic material on traditional superconductor is discussed through magnetic susceptibility,magnetization, and electron transport measurement. The five set of samples consist of same size of nickel nanoparticles with two different sizes of indium nanoparticles. Tc is reduced by interparticle proximity effect from neighboring magnetic particles. Furthermore, the electron transport reveals unusual two component behavior. Free electron model and Ginzburg-Landau theory are used to calculate GL parameter κ. Then according to the criterion of typeⅡ superconductor, the value of κ is greater than 1. From both the calculated κ value and two component behaviors, this system is classified to the typeⅡ-like superconductor. The diamagnetic signals of superconductivity in large particles are stronger than small ones.Interestingly, the small and large nanoparticles have shown entirely different physical properties. The small particle size sample shows the coexistence of superconductivity and hopping conduction at low temperature. Spin dependent magnetoresistance (MR) and negative MR at high applied magnetic field regime are observed at normal state and superconducting state respectively. In50-Ni50 is the sample in large particle size series. It shows diamagnetic superconducting signals under different applied magnetic field at below Tc. At temperature below 2.5K, magnetic susceptibility and magnetization increase with decreasing temperature which signals the existence of spin polarized moment. We attribute these behaviors to the coexistence of superconductivity and spin polarized moment. Moreover,the electron transport data exhibits superconductivity dependent double reentrant behavior and unconcerned with spin polarized magnetic moment.
顯示於類別:	[物理研究所] 博碩士論文

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