The pressure dependence of the magnetic and superconducting transitions and that of the superconducting upper critical field are reported for $\mathrm{CaK}{\left({\mathrm{Fe}}_{1-x}{\mathrm{Ni}}_x\right)}_4{\mathrm{As}}_4$, the first example of an Fe-based superconductor with spin-vortex-crystal-type magnetic ordering. Resistance measurements were performed on single crystals with two substitution levels $\left(x=0.033,0.050\right)$ under hydrostatic pressures up to 5.12 GPa and in magnetic fields up to 9 T. Our results show that, for both compositions, magnetic transition temperatures $T_{\mathrm{N}}$ are suppressed upon applying pressure; the superconducting transition temperatures $T_{\mathrm{c}}$ are suppressed by pressure as well, except for $x=0.050$ in the pressure region where $T_{\mathrm{N}}$ and $T_{\mathrm{c}}$ cross. Furthermore, the pressure associated with the crossing of the $T_{\mathrm{N}}$ and $T_{\mathrm{c}}$ lines also coincides with a minimum in the normalized slope of the superconducting upper critical field, consistent with a likely Fermi-surface reconstruction associated with the loss of magnetic ordering. Finally, at $p\sim 4$ GPa, both Ni-substituted $\mathrm{CaK}{\left({\mathrm{Fe}}_{1-x}{\mathrm{Ni}}_x\right)}_4{\mathrm{As}}_4$ samples likely go through a half-collapsed-tetragonal phase transition, similar to the parent compound ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$.

• Received 28 March 2018

DOI:https://doi.org/10.1103/PhysRevB.97.174517