  We described the effect of nonmagnetic impurity on the superconductivity
behavior of the NdFeAsO0.8F0.2 iron-based superconductor. The resistivity
measurement showed that the superconductivity suppressed upon increasing the
low amounts of calcium impurity (x<0.05). Also, the Tc decreased with the
increase in the residual resistivity. Such behavior was qualitatively described
by the Abrikosov-Gorkov theory and confirmed that these impurities act as
scattering centers. For our samples, the exchange constant between the calcium
and the conduction electron spins was estimated Jexc=|8| meV. Moreover, we
presented the phase diagram of our synthesized samples for the various calcium
dopings and found that according to increase of the calcium impurities and
temperature decreasing of the spin-density wave (TSDW), Fe ions arranged stripe
antiferromagnetically at lower temperatures and also the superconducting
transition temperature (TC) declined. Based on our results and in agreement
with the available theories as explained in the text, since the S++ state has
not an effect on the impurity doped samples, and the S+- state that is
attributed to the spin fluctuations mechanism causes the superconducting
suppression for low amounts of calcium. So, it confirms the role of the
spinfluctuations as a dominant pairing mechanism in our synthesized samples.
