High magnetic field phase diagram of PrOs4Sb12

Abstract

The magnetic phase diagram of PrOs${}_4$Sb${}_{12}$ has been investigated by specific heat measurements between 8 and 32 T. A new Schottky anomaly due to excitations between two lowest crystalline-electric-field (CEF) singlets, has been found for both $H\parallel (100)$ and $H\parallel (110)$ above the field where the field-induced ordered phase (FIOP) is suppressed. The constructed $H-T$ phase diagram shows weak magnetic anisotropy and implies a crossing of the two CEF levels at about 8 - 9 T for both field directions. These results provide an unambiguous evidence for the $\hat{I}{“}_1$ singlet being the CEF ground state and suggest the level crossing (involving lowest CEF levels) as the driving mechanism of FIOP.

Submitted to Phys. Rev. Lett