具AlB2結構之三元稀土化合物之電磁性研究

Abstract

在這份論文之中，我們製作了含稀土元素之合金 (R2NiGe3，R = Y、La、Ce、Pr、Nd、Sm、Gd、Dy、Ho)並成功地量測其結構與電磁性質。經由X-ray繞射結構分析，除了Sm的樣品為純相之外，其餘樣品之結構在靠近(101)處，含有一個來自於化學劑量比例為1:2:2的相，除此之外並無其它的額外多餘的相，因此我們相信其結構應為六角最密堆積的AlB2 結構。對於Y2NiGe3與La2NiGe3這兩個樣品，根據電阻率的資料顯示，在溫度低於1 K時，它們應該是超導體。而 Gd2NiGe3 與Dy2NiGe3則在低溫的時候，具有反鐵磁的特性。在電性方面，Ce2NiGe3這個樣品在低溫時(6 K~18 K)其電阻隨溫度下降而上升，而其電阻來自於磁性的部份，在300 K到80 K 隨溫度下降而上升，在低於6 K後，隨溫度下降而下降，這樣的行為與近藤晶格系統 (Kondo lattice system) 類似。

We have successfully synthesized the rare earth ternary intermetallics R2NiGe3 (R = Y, La, Ce, Pr, Nd, Sm, Gd, Dy, and Ho), which crystallized in a AlB2-derived hexagonal structure with space group P6/mmm as confirmed from the X-ray diffraction measurements. Except Sm2NiGe3, all the samples have additional peak which is due to a parasitic phase with the stoichiometry 1:2:2. Magnetic behavior and electrical resistivity are investigated on this compound. Curie-Weiss law is used to calculate the effective moments of the rare earth ions in the paramagnetic state. The magnetization measurements indicate that Y2NiGe3 and La2NiGe3 are not superconductors above 2 K, and the R2NiGe3 compounds (R = Gd, and Dy) ordered antiferromagnetically at low temperatures. For Ce2NiGe3 compound, the magnetic resistivity show as -lnT dependence from room temperature to 80 K and other portion of a very faint -lnT dependence from 20 K to 6 K. The magnetic resistivity increases as the temperature is lowered, instead of steadily decreasing, and decreases with the decrease of the temperature below 6 K, this magnetic contribution to the resistivity is similar to that of a Kondo lattice system.