Ultrasonic Study on the Hexagonal Antiferromagnet Dy₃Ru₄Al₁₂

Abstract

In the distorted kagome lattice antiferromagnet Dy3Ru4Al12 with TN = 7 K, a crystal electric field (CEF) effect is expected at high temperatures. To investigate the CEF effect and the phase transition at TN, we performed ultrasonic measurements on a single-crystalline sample. At high temperatures, both the longitudinal elastic modulus C11 and the transverse modulus C44 increase monotonically with decreasing temperature. Below 60 K a characteristic elastic softening is observed in C44 in contrast to C11 with monotonic hardening down to TN. We analyzed C44 using the Curie-Weiss-type equation and obtained a negative parameter: Θ which is proportional to a quadrupole-quadrupole coupling constant under the hexagonal CEF. With further decreasing temperature, both moduli exhibit abrupt elastic hardening at TN due to a magnetostriction.