Evolution of superconductivity and antiferromagnetic order in Ba(Fe_0.92-xCo_0.08V_x)₂As₂

The vanadium doping effects on the superconductivity and magnetism of iron pnictides are investigated in Ba(Fe_0.92-xCo_0.08V_x)₂As₂ by transport, susceptibility, and neutron scattering measurements. The doping of magnetic impurity V causes a fast suppression of superconductivity with T_C reduced at a rate of approximately 7.4 K/1% V. On the other hand, for x ≥ 0.02, long-range C-type antiferromagnetic order is recovered upon V doping, in contrast to the x = 0 sample with no detectable magnetic order. The value of ordered magnetic moments of Ba(Fe_0.92-xCo_0.08V_x)₂As₂ follows a domelike evolution versus doping concentration x. A possible Griffiths-type antiferromagnetic region of multiple coexisting phases in the phase diagram of Ba(Fe_0.92-xCo_0.08V_x)₂As₂ is identified, in accordance with previous theoretical predictions based on the cooperative behavior of magnetic impurities and conduction electrons mediating the Ruderman-Kittel-Kasuya-Yosida interactions between them.