Non-Kramers doublet ground state in a quaternary cubic compound PrRu2In2Zn18 investigated by ultrasonic measurements

Abstract

Abstract We performed ultrasonic measurements on a quaternary cubic compound PrRu2In2Zn18 to explore the ground state properties derived from non-Kramers Γ3 doublet of Pr3+. PrRu2In2Zn18 is a quaternary derivative of the ternary compound PrRu2Zn20 that exhibits a structural phase transition at T S = 138 K. In PrRu2In2Zn18, the Zn atoms at the 16c site in PrRu2Zn20 are selectively replaced by In atoms. A monotonic increase was observed in the temperature dependence of elastic constants C L = (C 11 + 2C 12 + 4C 44)/3 and C T = (C 11–C 12 + C 44)/3 in the temperature range around T S to which an elastic softening was observed in (C 11 – C 12)/2 for PrRu2Zn20. The disappearance of the softening indicates that the structural transition in PrRu2Zn20 is suppressed by the substitution of Zn ions by In ones with a larger ionic radius. Alternatively, the C T of PrRu2In2Zn18 exhibits a precursor Curie-type elastic softening toward low temperatures being responsible for the non-Kramers Γ3 ground state. We discuss the ground state and the evolution of the elastic properties of the different single-crystal samples of PrRu2In2Zn18 grown under different conditions.