銅氧平面上的雜質對超導弱鐵磁石RuSr2RCu2O8 ( R=Gd, Eu )超導性與磁性的影響

淡江大學機構典藏 > 理學院 > 物理學系暨研究所 > 學位論文 > Item 987654321/51780

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Title:	銅氧平面上的雜質對超導弱鐵磁石RuSr2RCu2O8 ( R=Gd, Eu )超導性與磁性的影響
Other Titles:	The effect of in-plane impurity on superconductivity and magnetism in superconducting weak ferromagnet RuSr2RCu2O8 ( R=Gd, Eu )
Authors:	吳尚倫;Wu, Shang-lun
Contributors:	淡江大學物理學系碩士班林大欽
Keywords:	超導弱鐵磁石;磁阻;反鐵磁;d-wave superconductivity;canted antiferromagnetism;magneto-transport
Date:	2010
Issue Date:	2010-09-23 16:05:24 (UTC+8)
Abstract:	我們利用固態反應法製作了Ni和Zn摻雜RuSr2R(Cu1-xMx)2O8 (R=Gd, Eu；M=Ni, Zn)的多晶塊材樣品，並且有系統地對其作了結構、電性、磁性、磁阻、X-ray吸收光譜的量測與分析。GSAS彌合X-ray的數據發現，銅氧平面的摻雜使系統中的釕氧八面體繞著c-軸集體式的旋轉角度變小，系統的晶體結構經歷一扭曲-非扭曲的轉變。對於鎳摻雜的樣品，摻雜量的增加對於超導轉變溫度的抑制程度，遵循A-G配對破壞理論的預測；然而，鋅摻雜的樣品，摻雜量的增加對於超導轉變溫度的抑制則偏離A-G配對破壞理論的預測。相對應地，摻雜量的增加造成Gd系列樣品和Eu系列樣品的磁有序轉變溫度分別往高溫和低溫移動。再者，磁阻比值在磁轉變溫度以上，隨著溫度的下降從正比於外加磁場兩次方漸漸變為正比於外加磁場一次方。當溫度低於磁轉變溫度，外加磁場小於2~3 Tesla時，會有正磁阻的出現；外加磁場大於2~3 Tesla時，則伴隨著負磁阻的出現，其中Gd系列樣品的負磁阻比值大於Eu系列樣品，顯示兩系列樣品在低溫、高磁場下的磁結構是截然不同的。X-ray吸收光譜實驗可得知釕是以四價/五價的混合態存在於樣品中。隨著摻雜量的增加，Gd系列樣品中的釕四價含量些許增加，Eu系列樣品的釕四價含量反而減少。 The polycrystalline bulk samples of RuSr2R(Cu1-xMx)2O8 (R = Gd, Eu，M = Ni, Zn) were synthesized by the solid-state reaction techniques, and have been extensively investigated for structure, magnetization, resistance, and MR ratio. In powder X-ray diffraction Rietveld refinement study, we found the doping of impurity make RuO6 octahedral distort and rotate about c-axis. The crystal structure may undergo a distorted-to-undistorted transition. The Tc suppression in Ni-doped samples displays a AG-like behavior, but it in Zn-doped samples doesn’t. With the increase of the impurity, the TM of doped samples of Ru-1212Gd and Ru-1212Eu become higher and lower respectively. In MR ratio measurement, MR ratio values are proportion to Hα with α=2 above 200 K, Below 200 K we find that α continuously decreases to a value of α=1 as the magnetic ordering temperature is approached. Furthermore, just below the magnetic ordering temperature, a positive magnetoresistance is observed for low applied magnetic fields. The positive magnetoresistance was interpreted as being due to orbital magnetoresistance or spin-flip. In higher applied magnetic field, we observe the negative magnetoresistance in doped Ru-1212Gd samples, but we still observe the positive magnetoresistance in doped Ru-1212Eu samples. It reveal that the magnetic crystal structures in doped Ru-1212Gd and doped Ru-1212Eu samples are obviously different below TM , It may account for that why the Tc suppression in Ni-doped and Zn-doped samples are distinct.
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