Pressure–temperature phase diagram of CeAg

•We performed electrical resistivity measurements under high pressure on ferrromagnet CeAg.•A pressure–temperature phase diagram of CeAg was revised above 2.1 GPa.•A phase boundary between a tetragonal and unknown phases may terminate at a critical end point.•The presence of a pressure-induced quantum critical point at around 6 GPa is suggested.

We have performed electrical-resistivity measurements under hydrostatic pressures ranging up to 4.47 GPa on the cubic compound CeAg. A pressure–temperature phase diagram has been revised in a high-pressure range above ∼2.1GPa, where the system is known to enter into an unidentified phase through a first-order phase transition. We have found that the electrical resistivity shows a clear kink anomaly below ∼ 4 K in this unknown phase. The anomaly shifts to lower temperature with increasing pressure, and shows a tendency to reach absolute zero at ∼6GPa, suggesting the presence of a pressure-induced quantum critical point around this pressure. We have also observed that a first-order phase boundary line, which separates the phase diagram into two regions of a tetragonal phase and the unidentified phase, seems to terminate in a critical end point located at (PCEPPCEP, TCEPTCEP) ∼(3.2GPa,200K). This suggests that the crystal symmetry of the unidentified phase above ∼2.1GPa is also tetragonal.