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. Tc 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 x 10(4)A cm(-2) and 3.2 x 10(3)A cm(-2) at 2 K and 25 K, respectively, at near zero field. These relatively high Jc 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.