Structural modulation and physical properties of cobalt-doped layered La₂M₅As₃O₂(M = Cu, Ni) compounds

We investigate the structural variation and physical properties of layered La2 M5As3O2 (M = Cu, Ni) compound upon Co doping. It is found that the substitution of Co ion just induces the monotonous change of lattice constants without observing the anomalous kink in superconducting La2(Cu1-xNix)5As3O2 solid-solutions. Meanwhile, this doping barely changes As-As bond length in [M5As3]2- subunit (±2%), being significantly smaller than 7% shrinkage of that in La2(Cu1-xNix)5As3O2. Therefore, the doping dependence of crystal structure exhibits similar trend with Ba1-xKxFe2As2 without the interference of As1-As2 bonding, implying that the Co substitution for Cu/Ni is hole-doped. In terms of physical property, La2(Cu1-xCox)5As3O2 turns into itinerant ferromagnetic metal, while La2(Ni1-xCox)5As3O2 shows paramagnetism and suppressed structural phase transition upon Co-doping. The distinct structural variation and absence of superconductivity provide important clues to understand the effect of As-As bond in [M5As3]2- subunit.