High-Field Phase Diagram of SmRu4P12 Determined by Ultrasonic Measurements in Pulsed Magnetic Field up to 55 T

Elastic constant measurements were performed for the filled skutterudite compound SmRu4P12 in a pulsed magnetic field up to 55 T of \(H\parallel\langle 111\rangle\) to create a high-field phase diagram. The field dependence of the transverse elastic constant \(C_{\text{T}} = (C_{11} - C_{12} + C_{44})/3\) shows two marked anomalies, one of which was assigned as a magnetic transition \(T^{*}\). The other anomaly was newly discovered. The newly discovered phase boundary is immersed in the known phase III, and joins to the known II–III boundary. This particular behavior is compared with the recently proposed theory, and discussed on the basis of the octupole model for this system.