H−Tphase diagram ofURu2Si2in high magnetic fields

Abstract

We have studied the ultrasonic velocity and ac susceptibility of ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$ in magnetic fields up to 45 T. The resulting phase diagram reveals new phase boundaries that place strong constraints on theories of hidden order for this material. Furthermore, a significant difference between the constructed $H\ensuremath{-}T$ phase diagram and that extracted from earlier pulsed field measurements is explained in terms of a large magnetocaloric effect. An offshoot of this analysis is that care should be taken in interpreting pulsed field measurements.