Ultrasonic Study On The Hexagonal Antiferromagnet Dy3ru4al12

In the distorted kagome lattice antiferromagnet Dy3Ru4Al12 with T-N = 7 K, a crystal electric field (CEF) effect is expected at high temperatures. To investigate the CEF effect and the phase transition at T-N, we performed ultrasonic measurements on a single-crystalline sample. At high temperatures, both the longitudinal elastic modulus C-11 and the transverse modulus C-44 increase monotonically with decreasing temperature. Below 60 K a characteristic elastic softening is observed in C-44 in contrast to C-11 with monotonic hardening down to T-N. We analyzed C-44 using the Curie-Weiss-type equation and obtained a negative parameter: circle minus which is proportional to a quadrupole-quadrupole coupling constant under the hexagonal CEF. With further decreasing temperature, both moduli exhibit abrupt elastic hardening at T-N due to a magnetostriction.