High magnetic field phase diagram of PrOs4Sb12

TL;DR

This study maps the magnetic phase diagram of PrOs4Sb12 under high magnetic fields, revealing a level crossing of CEF states that drives the field-induced ordered phase, with implications for understanding its electronic ground state.

Contribution

It provides the first detailed high-field phase diagram of PrOs4Sb12, confirming the CEF level crossing as the mechanism behind the FIOP and establishing the $ ext{Gamma}_1$ singlet as the ground state.

Findings

Identification of a new Schottky anomaly due to CEF excitations.

Weak magnetic anisotropy in the phase diagram.

Evidence for crossing of CEF levels at 8-9 T.

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 $\Gamma_1$ singlet being the CEF ground state and suggest the level crossing (involving lowest CEF levels) as the driving mechanism of FIOP.