Filling the holes in the CaFe4As3 structure: Synthesis and magnetism of CaCo5As3

Here, we investigate single crystals of CaCo₅As₃ by means of single-crystal x-ray diffraction, microprobe, magnetic susceptibility, heat capacity, and pressure-dependent transport measurements. CaCo₅As₃ shares the same structure of CaFe₄As₃ with an additional Co atom filling a lattice vacancy and undergoes a magnetic transition at T_M=16 K associated with a frustrated magnetic order. CaCo₅As₃ displays metallic behavior and its Sommerfeld coefficient (γ =70 mJ/mol K²) indicates a moderate enhancement of electron-electron correlations. Transport data under pressures to 2.5 GPa reveal a suppression of T_M at a rate of -0.008 K/GPa. First-principles electronic structure calculations show a complex three-dimensional band structure and magnetic moments that depend on the local environment at each Co site. Our results are compared with previous data on CaFe₄As₃ and provide a scenario for a magnetically frustrated ground state in this family of compounds.