Abstract
We report magnetic susceptibility, resistivity, and heat capacity measurements on single crystals of the Sr(FeCo)As and SrEu(FeCo)As series. The optimal Co concentration for superconductivity in Sr(FeCo)As is determined to be . On the basis of this, we grew members of the SrEu(FeCo)As series so as to examine the effects of well-defined, local magnetic moments on the superconducting state. We show that superconductivity is gradually suppressed by paramagnetic Eu doping and coexists with antiferromagnetic ordering of Eu as long as . For , crosses and the superconducting ground state (as manifested by zero resistivity) abruptly disappears with evidence for competition between superconductivity and local moment antiferromagnetism for up to 0.72. It is speculated that the suppression of the antiferromagnetic fluctuations of the Fe sublattice by coupling to the long-range order of the Eu sublattice destroys bulk superconductivity when .
5 More- Received 30 December 2010
DOI:https://doi.org/10.1103/PhysRevB.83.094520
©2011 American Physical Society