Robustness of superconductivity to competing magnetic phases in   tetragonal FeS
  We have determined the superconducting and magnetic properties of a hydrothermally synthesized powder sample of tetragonal FeS using muon spin rotation ({\mu}SR). The superconducting properties are entirely consistent with those of a recently published study, showing fully gapped behavior and giving a penetration depth of {\lambda}_{ab} = 204(3) nm. However, our zero-field {\mu}SR data are rather different and indicate the presence of a small, non-superconducting magnetic phase within the sample. These results highlight that sample-to-sample variations in magnetism can arise in hydrothermally prepared phases, but interestingly the superconducting behavior is remarkably insensitive to these variations. 
Franziska K. K. Kirschner, Franz Lang, Craig V. Topping, Peter J.   Baker, Francis L. Pratt, Sophie E. Wright, Daniel N. Woo...
cond-mat.supr-con cond-mat.str-el