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 $T_N\sim$ 88 K in CaFe${}_4$As${}_3$ changes only by up to $\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 $T_2\sim$ 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${}_{1-x}$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 $p_c\sim$ 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.

• Received 7 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.104444