Higher-Order Multipolar Effects on Elastic Properties of PrNi5

We have measured the elastic constants of PrNi 5 , which has a singlet ground state, Γ 4 , as a function of the temperature. The characteristic anomalies have been observed around 23 K in longitudinal C 11 and C 33 . The minimum temperature of C 11 and C 33 are higher than calculated results only with quadrupolar interactions. Therefore, we have used a magnetoelastic Hamiltonian with coupling of strains and higher-order multipoles in analysis. In C 11 and C 33 , the anomalies can be explained by the strain susceptibilities, which include the multipolar operators O 6 0 and O x y 4 .