金鎳奈米核殼結構的巨觀法拉第感應及磁性鬆弛研究

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题名:	金鎳奈米核殼結構的巨觀法拉第感應及磁性鬆弛研究
作者:	郭蓁蓁;Kuo,Chen-chen
贡献者:	物理學系
关键词:	金鎳奈米顆粒;核殼結構;磁性鬆弛;法拉第感應
日期:	2015-07-15
上传时间:	2015-09-23 11:33:44 (UTC+8)
出版者:	國立中央大學
摘要:	本論文討論Au@Ni核殼結構奈米顆粒的磁性研究與磁性鬆弛現象，使用氣相冷凝法的雙鍍源方式製備奈米顆粒，利用XRD和EDXS分析樣品成分與粒徑，得到顆粒平均粒徑約10 nm，與AFM影像分析結果相符。 Au@Ni奈米顆粒的磁滯現象持續到100 K，在1.8 K的矯頑磁場34 Oe，殘留的磁化強度0.3 emu/g。在低的外加磁場且溫度低於TB易見記憶效應，以Protocol 1的實驗條件可以看到Au@Ni奈米顆粒出現記憶效應。 Au@Ni奈米顆粒的磁性鬆弛研究，除發現磁化強度有翻轉及反轉的現象以外，量測的磁化強度初始值以及磁化強度隨時間的圖形變化，對於外在的實驗條件是敏感的，磁化強度翻轉的來源與樣品為核殼結構有關。磁化強度隨時間鬆弛的曲線，應有兩個分量的貢獻，分別是殘留的磁化強度Mi曲線和感應的磁化強度Mr曲線。 Au@Ni奈米顆粒的磁性鬆弛現象，除與溫度、外加磁場有關以外，還受到降溫過程、降場速率、外加磁場時間、磁性量測的影響。;We report on the magnetic properties and magnetic relaxation behaviors in nano-sized core@shell structure of Au@Ni. The Au@Ni NPs were fabricated employing the gas-condensation method, using a chamber equipped with two decoupled evaporation sources for separate evaporation of Ni or Au. We have X-ray diffraction patterns and EDXS spectra, resulting in a mean particle diameter of 10 nm for the Au@Ni, which agrees well with that was obtained from the AFM images. Magnetic hysteresis can be clearly seen in the M(Ha) curves taken below 100 K, with a coercivity of HC = 34 Oe and a low remanence of Mr = 0.3 emu/g at 1.8 K. Memory effect can be clearly seen in protocol 1, indicating that low Ha and below TB is important for memory effect. The large inverse remanent magnetization is very sensitive to the field reduction rate as well as to the thermal and field processes before turning the Ha off. Spontaneous reversal in direction and increase in magnitude of the remanent magnetization in subsequent relaxation through time were found. All various types of the temporal relaxation curves of the remanent magnetizations are successfully scaled by a relaxation time to describe the reduction rate together with a dynamic exponent to describe the dynamical slowing down of the relaxation through time evolution. The key to these effects is to have the induced eddy current running beneath the amorphous Ni shells through Faraday induction.
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