Pressure-temperature phase diagram of CaK(Fe1-xMnx)4As4 (x=0.024)

Resistance measurements on single crystals of CaK(Fe1-xMnx)4As4 (x = 0.024) were performed under hydrostatic pressure up to 5.15 GPa. The pressure dependence of the magnetic and superconducting transition temperatures and that of the superconducting upper critical field are reported. Our results show that upon increasing pressure, the magnetic transition temperature TN is suppressed, whereas the superconducting transition temperature Tc first increases and then decreases, exhibiting a maximum at a pressure pc corresponding to the intersection of the TN(p) and Tc(p) lines. In addition, a minimum in the normalized slope of the superconducting upper critical field as well as a change in the pressure dependence of the inferred superconducting coherence length are observed at pc, suggesting a difference in the Fermi surface of the paramagnetic and antiferromagnetic states. Finally, CaK(Fe1-xMnx)4As4 (x = 0.024) likely goes through a half-collapsed tetragonal phase transition at -4.3 GPa, further demonstrating that the half-collapsed tetragonal transition pressure in the CaKFe4As4 system is relatively insensitive to transition metal substitution.