New oxypnictide superconductors: PrOFe1−xCoxAs

Oxypnictides of the type PrOFe1−xCoxAs (x≤0.3) were synthesized for the first time by the sealed tube method. All the compounds were found to be monophasic and crystallize in the tetragonal ZrCuSiAs type structure (space group=P4/nmm) and the lattice parameters (a and c) decrease with increase in cobalt content. Mössbauer measurements of the compounds indicate low spin Fe2+ in tetrahedral coordination. Resistivity and magnetization studies reveal superconducting transitions in compounds with ‘x’=0.05, 0.10 and 0.15, with maximum transition temperature (Tc) at ∼14 K in the compound with ‘x’=0.1. The variation of resistivity with temperature under different magnetic field has been studied to estimate the upper critical field (Hc2) (∼50.2 T for the ‘x’=0.1 composition). The Seebeck and Hall coefficient (RH) suggests electron type charge carriers in these compound and the charge carrier density increases with increase in Co-doping.

Cobalt doping at the iron site in PrOFeAs (semimetal) compound suppresses structural distortion and spin density wave with the evolution of superconductivity. The Seebeck and Hall coefficient (RH) indicate electron type charge carriers in these compounds and charge carrier density increases with increase in Co-doping. Temperature dependence of resistivity (ρ) for (a) PrOFeAs, (b) PrOFe0.95Co0.05As, (c) PrOFe0.9Co0.1As, (d) PrOFe0.85Co0.15As, (e) PrOFe0.8Co0.2As and (f) PrOFe0.7Co0.3As.Figure optionsDownload as PowerPoint slide