Superconductivity and Paramagnetism in the Nd-Based 1111 Oxypnictide Compounds

NdFeAsO
_0.82
F
_0.18
and NdFe
_0.88
Co
_0.12
AsO polycrystalline samples are characterized by magnetic measurements as a function of the temperature under different applied fields that are in the range of 0.002-4.0 T. As the applied field is increased, a paramagnetic contribution hides the superconducting transition in both samples. We remove the paramagnetic contribution either by subtracting the signal from a NdFeAsO sample or from a Curie-Wise fitting. Both methods allow us to reveal the superconducting transition, but the first one works a little better. This indicates that in these Nd-based 1111 superconductors, the paramagnetic contribution is related to the Nd
³⁺
ions in the 1111 structure and, that in the doped compounds the two states, superconductivity and paramagnetism coexist.