Tricritical Phenomena at the Cerium γ→ α Transition

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The γ→ α isostructural transition in the Ce₀.₉₋ₓLaₓTh₀.₁ 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 ≤ xc ≤ 0.14. At the tricritical point, the coefficient of the linear T term in the specific heat γ 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 xc, the Wilson ratio, RW, 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.