三元稀土合金R8CoGa3(R = 釔及稀土元素)之結構、電性與磁性研究

Abstract

三元稀土合金R8CoGa3(R = 釔及稀土元素)，結構為六角晶系，空間群為P63mc 與Space No. 186。晶格常數由La8CoGa3的a = 11.05 A and c = 7.064 A隨著稀土元素的原子量增加減少。 這個系列R8CoGa3的電阻率量測範圍由室溫的300 K量測到低溫約4~5 K。La8CoGa3這個樣品在6 K顯示典型的超導相轉換。而對於R = Ce, Pr, Nd, Gd, Dy, Ho的樣品們，電阻率隨著溫度下降而上升，分別在不同的溫度顯現出電阻極大值。而Y8CoGa3這個樣品則在溫度為155 K時顯示出電阻極小值。部分的樣品的雌性電阻在某些溫度區間有「-lnT」¬的傾向，這可能與「近藤效應(Kondo effect)」有關。¬ 在磁化率的量測部分，量測了R = La, Ce, Pr, Nd的樣品。在La8CoGa3的部分，量測出來發現磁化率在4 K的部分有超導的現象，和電阻量測的6 K超導溫度並不相同。Ce8CoGa3和Pr8CoGa3顯示出反鐵磁性，Nd8CoGa3而則是顯示出鐵磁性。

These R8CoGa3 (R = Y and rare earth atoms) compounds crystallize in the hexagonal structure with space group P63mc (Space No. 186). The obtained values of the lattice parameters are a = 11.05 A and c = 7.064 A for La8CoGa3. Both the values of a and c are found decreasing monotonically with increasing atomic number of the rare earth ions. The temperature dependence of electrical resistivity ρ(T) below room temperature of the R8CoGa3 have been investigated. The ρ(T) curve of La8CoGa3 shows a typical superconducting phase transition at 6 K. The electrical resistivity of R8CoGa3 (for R = Ce, Pr, Nd, Gd, Dy, Ho) are found increasing with decreasing temperature T from room temperature and reveal local maximum. The ρ(T) of Y8CoGa3 shows a local minimum at 155 K. The magnetic resistivity of some compounds show “-lnT” dependence which may due to the Kondo effect. The susceptibility measurements are done for R = La, Ce, Pr, Nd. For La8CoGa3, superconducting transition is observed but at 4 K which differs from 6 K. It shows the antiferromagnetic correlation in the paramagnetic state for Ce8CoGa3 and Pr8CoGa3 While for Nd8CoGa3, it shows the ferromagnetic correlation in the paramagnetic state.