Elastic Properties of Cage Compound CeOs2Al10

To investigate an origin of the novel phase transition at T 0 = 28.5 K in the cage compound CeOs 2 Al 10 , we measured temperature dependences of elastic moduli. We found a sudden elastic hardening below T 0 in all moduli and an abrupt elastic softening at T 0 in C 11 and C 22 . These behaviors in CeOs 2 Al 10 are almost similar to the elastic behaviors in CeRu 2 Al 10 , suggesting similarity of the phase transition among them. The magnitude of hardening in C L011 is the largest in the longitudinal moduli. Our results suggest that the phase transition is not simple magnetic one and the strain strongly couples to an order parameter. We estimated the strain dependence of T 0 along the a - and b -axes from the Ehrenfest relation, and that along the b -axis is the largest.