Unexpected impact of magnetic disorder on multiband superconductivity

We analyze how the magnetic disorder affects the properties of the two-band s sub(+ or -) and s sub(++) models, which are the subject of discussions regarding iron-based superconductors and other multiband systems like MgB sub(2). We show that there are several cases when the transition temperature T sub(c) is not fully suppressed by magnetic impurities in contrast to the Abrikosov-Gor'kov theory, but a saturation of T sub(c) takes place in the regime of strong disorder. These cases are: (1) the purely interband impurity scattering and (2) the unitary scattering limit. We show that in the former case the s sub(+ or -) gap is preserved, while the s sub(++) state transforms into the s sub(+ or -) state with increasing magnetic disorder. For case (2), the gap structure remains intact.