- 學位論文
鐵磁超導體釕鍶釓銅氧與鐵基釤鐵鉮氧化合物之物理性質及其磁各向異性之研究
Physical Properties and Magnetic Anisotropy in Ferromagnetic Superconductor RuSr2GdCu2O8 and Iron-based SmFeAsO system
摘要
本論文為鐵磁超導體釕鍶釓銅氧與鐵基釤鐵鉮氧氟化合物之物理性質及其各向異性之研究。 本文研究的第一部分為鐵磁超導體之釕銅化合物，在釕鍶銅氧化合物(RuSr2RCu2O8, R = Pr, Nd, Sm, Eu, Gd)之系統中，當稀土元素為釓Gd與銪Eu可形成鐵磁超導體，此類超導體有其特殊性，隨溫度的變化發生磁性與電性的相轉變,由溫度300 K 逐漸降低，依序為順磁金屬態、鐵磁金屬態、超導態，釕鍶釓銅氧化合物(RuSr2GdCu2O8)的磁有序轉變溫度131 K 由Ru5+/4+ 離子長程有序所造成，低溫時發生超導態轉變Tc(dia) 39 K為銅氧平面所造成。系統存在由釕離子所自發的鐵磁有序與銅氧平面發生超導的晶體結構，由電性與磁性的量測，建構此化合物的電子狀態相圖，並以不同稀土元素取代來研究其結構轉變、磁性、比熱及電性等性質，金屬絕緣體相轉變邊界發生在釤Sm附近。磁場下旋轉排序的釕鍶銅氧化合物(RuSr2RCu2O8)粉末樣本，研究鐵磁超導體的各向異性。 本文研究的第二部分為鐵基超導體之鐵鉮化合物，在釤鐵鉮氧化合物(SmFeAsO)系統中，SmFeAsO在電性上有一個轉變溫度140 K，氟掺雜後的SmFeAs(O0.6F0.2)樣本，其晶胞體積縮小，進而發生超導Tc (zero) = 20 K。在磁場下排序超導的Tc = 52 K鐵鉮化合物(Sm0.95La0.05)FeAs(O0.85F0.15)粉末樣本，研究鐵鉮超導體的磁性各向異性300 K順磁態時gamma = x_c/x_ab = 0.83，低溫2 K超導態時 gamma= 3。 微晶粒在磁場中的晶向排序法是基於微晶粒的磁各向異性來達成。磁各向異性的發生與原子內的電子自旋和原子間的軌道偶合有關。此晶向有序排列的樣品可以用來研究材料順磁、超導、吸收能譜之各向異性。
並列摘要
In this research, we studied the physical properties and their anisotropy of ferromagnetic superconductor RuSr2GdCu2O8 and iron-based SmFeAs(O1-x,Fx). Both compounds exhibit superconductivity at low temperature. For RuSr2GdCu2O8, the ferromagnetic transition at Tmag(Ru5+/4+) = 131 K and the superconducting transition at Tc(dia) = 39 K in CuO2 plane were observed. A lower transition with TN(Gd) = 2.5 K was also observed. A phase diagram was generated from resistivity and magnetic measurements. The crystal structure, magnetism, specific heat, and electric property were discussed. A metal-insulator transition boundary around Sm was observed. Further study was carried out to investigate the anisotropy of the ferromagnetic superconductor. For the semimetal SmFeAsO, a transition temperature of 140 K was obtained. The superconducting onset temperature Tc(onset) of 40 K and zero resistivity Tc(zero) of 20 K were observed for SmFeAs(O0.6F0.2) sample. Due to spin-orbit related anisotropy in paramagnetic susceptibility, ab(Fe) > c(Fe) at 300 K in (Sm0.95La0.05)FeAs(O0.85F0.15) powder, a grain-aligned sample can be achieved using field-rotational method. The anisotropy of 0.83 in the paramagnet at 300 K increased to 3 in the superconducting state at 2 K. The grain alignment in magnetic field was based on the principle of magnetic anisotropy which is relative to the spin order with the orbit order of grain. The spin order drives orbit order of the grain. The sample of aligned grains was studied for anisotropic paramagnet, anisotropic superconductivity, and anisotropic X-ray absorption near edge spectra.
參考文獻
延伸閱讀
- Tsai, C. Y. (2009). 在鈦酸鉛及氧化鐵鈷的多重鐵性系統中研究受應力影響之介面聲子與鐵磁特性 [master's thesis, National Chiao Tung University]. Airiti Library. https://doi.org/10.6842/NCTU.2009.00452
- 吳奇錕（2007）。鐵酸鉍與鈷鐵氧體之複合材料電性與磁性研究〔碩士論文，國立清華大學〕。華藝線上圖書館。https://doi.org/10.6843/NTHU.2007.00175
- 李曉燕（2010）。具磁性奈米結構之氧化鐵/共軛高分子複合材料之合成、性質與應用〔博士論文，國立臺北科技大學〕。華藝線上圖書館。https://doi.org/10.6841/NTUT.2010.00126
- Johnston, D. C., Borsa, F., Cho, B. K., Canfield, P. C., Dervenagas, P., Goldman, A. I., Harmon, B. N., Miller, L. L., Stassis, C., Suh, B. J., Torgeson, D. R., Xu, M., Zarestky, J., Hundley, M. F., Movshovich, R., Thompson, J. D., Chubukov, A. V., & Sternlieb, B. (1996). Superconducting and Normal State Magnetic Properties of RNi2B2C Single Crystals. Chinese Journal of Physics, 34(2S), 397-405. https://www.airitilibrary.com/Article/Detail?DocID=05779073-199604-201212030010-201212030010-397-405
- Ku, H. C., Hsu, T. I., Hsu, Y. Y., Leer, T. J., Yeh, K. W., Huang, Y., Lin, J. Y., Chen, S. J., Yang, H. D., Chen, Y. Y., Ho, J. C., & Li, X. G. (1997). Anisotropic Magnetic and Calorimetric Properties of the Incommensurate Modulated Bi2Sr2PrCu2O8+δ Single Crystal. Chinese Journal of Physics, 35(6S), 903-908. https://www.airitilibrary.com/Article/Detail?DocID=05779073-199712-201211120004-201211120004-903-908