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

Abstract We performed ultrasonic measurements on a quaternary cubic compound PrRu 2 In 2 Zn 18 to explore the ground state properties derived from non-Kramers Γ 3 doublet of Pr 3+ . PrRu 2 In 2 Zn 18 is a quaternary derivative of the ternary compound PrRu 2 Zn 20 that exhibits a structural phase transition at T S = 138 K. In PrRu 2 In 2 Zn 18 , the Zn atoms at the 16 c site in PrRu 2 Zn 20 are selectively replaced by In atoms. A monotonic increase was observed in the temperature dependence of elastic constants C L = ( C 11 + 2 C 12 + 4 C 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 PrRu 2 Zn 20 . The disappearance of the softening indicates that the structural transition in PrRu 2 Zn 20 is suppressed by the substitution of Zn ions by In ones with a larger ionic radius. Alternatively, the C T of PrRu 2 In 2 Zn 18 exhibits a precursor Curie-type elastic softening toward low temperatures being responsible for the non-Kramers Γ 3 ground state. We discuss the ground state and the evolution of the elastic properties of the different single-crystal samples of PrRu 2 In 2 Zn 18 grown under different conditions.