R8CoAl3 (R = Y, La - Ho)以及RNiAl3 (R = Y, Sm - Ho) 三元稀土化合物之物性研究

Structure and Electrical properties of R8CoAl3 (R = Y and rare-earth ions) and RNiAl3 (R = Y, and Sm - Ho) compounds

張鈞皓(Chun-Hao Chang)

指導教授 ： 陳政維

國立臺灣大學/理學院/物理研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.01486

摘要

在這篇論文中，我們合成了稀土元素化合物R8CoAl3 (R = Y, La - Ho) 以及RNiAl3 (R = Y, Sm - Ho) ，並測量了其電阻與磁化率。經由X-ray 繞射結構分析，我們發現R8CoAl3的樣品會形成單相的Pr8CoGa3結構，而RNiAl3則會形成YNiAl3的結構。
對於R8CoAl3的電阻來說，我們並沒有看到整個系統一致性的行為。但是卻可以大致分成La8CoAl3和Ce8CoAl3、Nd8CoAl3和Sm8CoAl3以及Gd8CoAl3和Dy8CoAl3。其中La8CoAl3和Ce8CoAl3 都會出現類似自旋密度波的電阻表現。而Nd8CoAl3和Sm8CoAl3都會出現兩個轉折，可能代表了兩個磁相變。最後，Gd8CoAl3 和Dy8CoAl3都出現了類似Kondo 的 –lnT 的電阻變化。另外，La8CoAl3 在6 K左右顯示典型的超導相轉變。
對於RNiAl3的電阻來說，除了YNiAl3，整個系統在低溫的時候都會出現由磁性變化造成的轉折。而對TbNiAl3和DyNiAl3的電阻來說，在更低溫的時候會出現第二個轉折。這個轉折可以對應到磁化率的高點，可能代表了一個反鐵磁的相變。而HoNiAl3在低溫的時候會出現一個階梯狀的表現，這對應到了磁化率在17 K處形成的轉折，可能是由於結構變化造成的。

關鍵字

稀土元素 ； 三元合金 ； 近藤效應 ； 超導 ； 自旋密度波

並列摘要

The crystal structure, electrical, and magnetic properties of the series of rare earth ternary intermetallic compounds R8CoAl3 (R = Y, La-Ho) and RNiAl3 (R = Y, Sm-Ho) have been investigated using powder X-ray diffraction, electrical resistivity, and magnetic susceptibility measurements. X-ray diffraction patterns reveals that R8CoAl3 compounds crystallizes in Pr8CoGa3 type structure with space group P63mc. Whereas RNiAl3 compounds crystallizes in YNiAl3 type structure with space group Pnma.
The temperature dependent both magnetic susceptibility χ(T) and resistivity ρ(T) curves of La8CoAl3 shows a superconducting transition at 6 K. The Ce8CoAl3 compound shows a sudden upturn which may due to the spin density behavior. The resistivity behavior of other R8CoAl¬3 compounds shows quite different with each other. The Nd8CoAl3 and Sm8CoAl3 both show two changes of slopes in the ρ(T) curve. While, ρ(T) curves for Gd8CoAl3 and Dy8CoAl3 are exhibits show Kondo-like behavior at low temperature.
The RNiAl3 compounds, the resistivity and magnetic susceptibility measurement suggest that the magnetic transitions are quite complicated. The χ(T) curve for GdNiAl3 shows multiple transition at ~ 175 and 75 K, where ρ(T) curve shows a slope change and sharp drop, respectively. The χ(T) curve for HoNiAl3 shows a deviation of ZFC and FC around 27 K. Furthermore, there is a maximum around 23 K and a slope change around 16 K in the ZFC curve. But the YNiAl3 compound is nonmagnetic.

並列關鍵字

rare earth compound ； ternary alloy ； Kondo effect ； superconductivity ； spin density wave

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