Tricritical Phenomena at the Cerium ${\hat{I}}^3\to \hat{I}\pm$ Transition

Abstract

The ${\hat{I}}^3\to \hat{I}\pm$ isostructural transition in the Ce${}_{0.9-x}$La${}_x$Th${}_{0.1}$ system is measured as a function of La alloying using specific heat, magnetic susceptibility, resistivity, thermal expansivity/striction measurements. A line of discontinuous transitions, as indicated by the change in volume, decreases exponentially from 118 K to close to zero with increasing La doping and the transition changes from being first-order to continuous at a critical concentration $0.10\le x_c\le 0.14$. At the tricritical point, the coefficient of the linear $T$ term in the specific heat ${\hat{I}}^3$ and the magnetic susceptibility start to increase rapidly near $x$ = 0.14 and gradually approaches large values at $x$=0.35 signifying that a heavy Fermi-liquid state evolves at large doping. Near $x_c$, the Wilson ratio, $R_W$, has a value of 3.0, signifying the presence of magnetic fluctuations. Also, the low-temperature resistivity shows that the character of the low-temperature Fermi-liquid is changing.