Elastic anomalies at successive phase transitions in NdRu2Al10

Abstract

We carried out ultrasonic measurements on NdRu2Al10 single crystals in order to clarify what kind of phase transition occurs in this compound. The elastic moduli were measured as a function of temperature from 0.5 K to 150 K using the phase comparison-type pulse echo method. As the temperature is decreased from 150 K, longitudinal elastic modulus C11 and transverse elastic modulus C44 show a monotonic enhancement. With further decreasing temperature, both elastic moduli show abrupt hardening at 2.4 K and then show two-step softening at 1.3 K and 1.0 K. We found obvious hysteresis around both transitions at 1.3 K and 1.0 K in the temperature sweep, whereas no hysteresis was observed around the transition at 2.4 K within our experimental accuracy. The abrupt hardening at 2.4 K is very similar to that found in CeRu2Al10 and CeOs2Al10, suggesting that the transition at 2.4 K originates from the same mechanism of the transitions in CeRu2Al10 and CeOs2Al10. This is the first report that NdRu2Al10 undergoes the successive phase transitions.