Co and Mn doping effect in polycrystalline (Ca,La) and (Ca,Pr)FeAs₂ superconductors

The superconducting properties of Mn and Co doped (Ca,RE)FeAs₂ ((Ca,RE)112: RE = La, Pr) were investigated. Co doping increased T_c of (Ca,Pr)112 while Mn doping suppressed the superconductivity of (Ca,RE)112. The Co doped (Ca,La)112 exhibited a large diamagnetic screening, as well as sharper superconducting transition than Co-free (Ca,La)112. T_c  ^zero observed in the resistivity measurements increased from 14 to 30 K by Co doping, while ${T_c}^{onset}$ was not increased. The critical current density, J_c, of Co doped (Ca,La)112 was approximately 2.1 × 10⁴ A cm⁻² and 3.2 × 10³ A cm⁻² at 2 K and 25 K, respectively, at near zero field. These relatively high J_c values and large diamagnetic screening observed in the susceptibility measurements of the polycrystalline bulks are evidence that Co doped (Ca,RE)112 compounds possess bulk superconductivity. (paper)