RE2Cu0.8Ge3和R2CuAl3(R=鑭系金屬)三元稀土化合物之物性研究

Abstract

本篇論文報告了我們所研究的兩個系列三元稀土金屬間化合物RE2Cu0.8Ge3 (RE = 稀土元素) 和 R2CuAl3(R = 稀土元素)的傳導及磁性等物理特性。 藉由X光繞射結構分析，所有的樣品都為單相，晶胞的體積隨著稀土元素的原子序增加而逐漸變小，符合鑭系收縮的現象。 電阻率的量測得知每一樣品都與一般金屬類似，在低溫時圖形的轉折點顯示了該溫度處具有相的變化。 磁性方面，我們發現絕大多數的樣品在低溫的時候會有自旋玻璃凍結的現象，同時每個樣品個別發生鐵磁性或反鐵磁性的相轉變。

We have investigated the structure, transport and magnetic properties of the ternary compounds RE2Cu0.8Ge3 (RE = Rare earth ions) and R2CuAl3 (R = Nd, Sm, Gd, Tb, Dy, Ho and Er) by means of the X-ray diffraction, electrical resistivity ρ(T), dc magnetic susceptibility (T) measurements. The RE2Cu0.8Ge3 (RE = La, Ce, Pr, Nd, and Sm) compounds are found to crystallize tetragonalα-ThSi2 structure with space group I41/amd as confirmed from the X-ray diffraction measurements. The refined lattice parameters follows lanthanide contraction, it varies from a = 4.274, c = 14.486 A (La) to a = 4.130, c = 14.203 A (Sm). Whereas RE = Gd, Tb, Dy, Ho, and Er shows a superstructure ofα-ThSi2. It appears that the copper network in RE2Cu0.8Ge3 compounds show some vacancies. The magnetization measurements indicate that RE2Cu0.8Ge3 have spin-glass behavior, due to nonmagnetic-atom-disorder and vacancies except for RE = La. Magnetic ordering are observed in RE2Cu0.8Ge3 as revealed from theρ(T) and (T) curves. The Neel temperatures for compounds scale with the de Gennes factor which suggests that the primary mechanism of interactions leading to the ordering of the magnetic moments may be the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction. For R2CuAl3 compounds, they crystallized in MgCu2-type cubic structure (space group Fd-3m). The refined lattice parameters are found to decrease monotonically from 7.897 (Nd) to 7.716 A (Er). Magnetic ordering are observed in R2CuAl3 as revealed from theρ(T) and (T) curves.