Effects of chemical doping and pressure on CaFe4As3

The effects of chemical doping by P, Yb, Co, and Cu, and hydrostatic pressure on CaFe${}_{4}$As${}_{3}$, were studied on single-crystalline samples. While the former two dopants substitute the nonmagnetic ions, the latter two partially occupy the Fe sites within the magnetic sublattice. The incommensurate spin density wave (IC-SDW) ordering at ${T}_{N}\ensuremath{\sim}$ 88 K in CaFe${}_{4}$As${}_{3}$ changes only by up to $\ensuremath{\sim}$40% with doping and applied pressure. Thus the IC-SDW state appears more robust than in the layered Fe pnictides. The commensurate SDW (C-SDW) state below ${T}_{2}\ensuremath{\sim}$ 26 K is suppressed in the Co-doped series, while it moves up in temperature in the P-, Yb-, and Cu-doped compounds. A new magnetic phase transition is observed at an intermediate temperature ${T}_{3}$ in Ca(Fe${}_{1\ensuremath{-}x}$Co${}_{x}$)${}_{4}$As${}_{3}$. Resistivity and magnetization measurements on CaFe${}_{4}$As${}_{3}$ were performed under hydrostatic pressure up to 5 GPa, showing a systematic decrease of ${T}_{N}$ and a domelike phase boundary at ${T}_{2}$ up to ${p}_{c}\ensuremath{\sim}$ 2.10 GPa. At higher pressures, a possible structural phase transition occurs, marked by a slowly increasing transition temperature. A phase diagram is shown to compare the effects of chemical doping and pressure.