Anomaly of specific heat in high quality single crystal of PrAg₂In

PrAg₂In has a non-Kramers doublet Λ₃ ground state, which is expected to show a quadrupolar phenomena. Although many studies have been devoted to investigate the novel features of PrAg₂In, there is no clear result how to remove the degeneracy of quadrupolar moment because this compound has a Heusler structure, in which the substitution between Pr and In ions is inevitable. We therefore prepare a high quality single crystal of PrAg₂In with the residual resistivity ratio of 14, which is much larger than that of the previous samples. We measure the magnetic susceptibility with the SQUID magnetometer down to T 0.4 K and the specific heat in the magnetic fields up to H 8T along [100] crystal direction down to T =0.1 K. The susceptibility is consistent with the CEF calculation. The specific heat shows a sharp peak at around T_p 0.33 K. When the magnetic field is applied, the peak at T_P does not move up to H 2.5 T. In contrast, it shifts to higher temperatures with broadening above H 2.5 T. The broad peak above H 2.5 T is well reproduced by the Schottky specific heat due to the splitting of the Λ₃ doublet in the magnetic fields. From these results, we conclude that a phase transition related to the r3 doublet occurs at around T_P.