T-H phase diagram of PrPb₃ in [001] and [110] magnetic field directions

We have measured the magnetic field dependence of the specific heat in PrPb3 for H || [001] and [110] up to H = 8T. At H = 0T, a sharp λ-type peak due to antiferro-quadrupolar(AFQ) ordering and a small anomaly appears at TQ = 0.43K and T^* = 0.25K, respectively. The field dependence of TQ shows a reentrant behavior and a high-field phase appear above H ∼ 6 T in the both field directions. T^* shows a large difference between H || [001] and [110], suggesting that the anomaly is related to the anisotropic feature of the quadrupolar moment in magnetic fields. From these results, we describe the T-H phase diagram PrPb3 in H || [001] and [110].