Transport and magnetic properties of yttrium doped NdFeAs(O,F) superconductor

The transport and magnetic properties of the undoped and yttrium doped NdFeAs(O,F) superconductor are investigated in detail for the first time. The transition temperatures of the yttrium doped samples are found to increase monotonically and attain a maximum of 53.3 K for 30% yttrium doping, ∼4 K higher as compared to the yttrium free sample. The T C values observed from the temperature dependent ac susceptibility measurements are also in agreement with the resistivity measurements. Yttrium doping is found to decrease the lattice parameters of the system; causing an inner chemical pressure and thereby accomplishing a T C enhancement. Moreover, the substitution of relatively smaller yttrium ion at Nd site creates lattice defects which act as effective pinning centers thereby enhancing the J C ( H ) performance of the system.