Magnetic Phase Diagram of the Heavy Fermion Superconductor PrOs4Sb12

Abstract

We investigated the magnetic phase diagram of the first Pr-based heavy fermion superconductor PrOs 4 Sb 12 by means of high-resolution dc magnetization measurements in low temperatures down to 0.06 K. The temperature dependence of the magnetization M ( T ) at 0.1 kOe exhibits two distinct anomalies at T c1 =1.83 K and T c2 =1.65 K, in agreement with the specific heat measurements at zero field. Increasing magnetic field H , both T c1 ( H ) and T c2 ( H ) move toward lower temperatures without showing a tendency of intersecting to each other. Above 10 kOe, the transition at T c2 ( H ) appears to merge into a line of the peak effect which is observed near the upper critical field H c2 in the isothermal M ( H ) curves, suggesting a common origin for these two phenomena. The presence of the field-induced ordered phase (called phase A here) is confirmed for three principal directions above 40 kOe, with the anisotropic A-phase transition temperature T A : T A [100] > T A [111] > T A [110] . The present results are discussed on the basis of crystalline-electrical-field level schemes with a non-magnetic ground state, with emphasis on a Γ 1 singlet as the possible ground state of Pr 3+ in PrOs 4 Sb 12 .