Ultrasonic measurements at the metamagnetic transition in URu2Si2

Ultrasonic velocity measurements were performed on a single crystal of URu2Si2 at various temperatures in the 20 ms 50T pulsed magnets at the NHMFL, Los Alamos, NM. At 4 K a three-fold splitting of the metamagnetic transition is seen; corresponding features were observed earlier in magnetization studies. As the temperature is raised, the three-fold splitting evolves first into two features, then into a single broad dip, after which it disappears entirely.