Charge Density Wave and Magnetic Transitions in the Rare-Earth Ternary Intermetallic Compounds

• Main Authors: R. C. Yang, 楊榮清
• Other Authors: J. W. Chen
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/30028919975301029714

博士 === 國立臺灣大學 === 物理學研究所 === 91 === We have investigated the magnetic behavior, electrical resistivity, and specific heat on a series of the intermetallic compounds RNiX2, where R = La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm; X = C and Si. These compounds crystallize in the orthorhombic CeNiX2- type structure. Bulk superconductivity was observed in LaNiC2 with a superconducting transition temperature of 3.5 K. Except for LaNiC2 and CeNiC2, the light and heavy rare-earth (Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Y) RNiC2 compounds exhibit charge density wave behavior as revealed from the (T) data. In addition, most of the RNiC2 samples (except R = Pr) become magnetically ordered at low temperatures as revealed from the appearance of features in (T) curves and changes of the slopes in the (T) curves. The specific heat data also shows the match up characteristics to the magnetic and resistivity results. The magnetic ordering was observed in low temperature for all the compounds of silicide series containing magnetic rare earth elements. The compounds with R = Pr and Nd are ferromagnets while those containing R = Sm, Gd, Tb, Dy, Ho, Er and Tm are antiferromagnets with TN below 35 K. Some of these samples exhibit multiple magnetic transitions. Most of the compounds (R = Pr, Sm, Tb, Dy, Ho, Er, and Tm) containing the magnetic rare earth elements approximately show an entropy change of Rln2 for magnetic transition, which implies a doublet ground state. The change of magnetic entropy and the magnetic heat capacities of this series indicate a strong influence of the crystalline electric field on these compounds. The heavy rare earth compounds of RNiX2 are suitable materials for the magnetic regenerator, which exhibits large heat capacities in low temperature.