Suppression of superconductivity in Nb by IrMn in IrMn/Nb bilayers

Effect of antiferromagnet on superconductivity has been investigated in IrMn/Nb bilayers. Significant suppression of both transition temperature (T_c) and lower critical field (H_c1) of Nb is found in IrMn/Nb bilayers as compared to a single layer Nb of same thickness; the suppression effect is even stronger than that of a ferromagnet in NiFe/Nb bilayers. The addition of an insulating MgO layer at the IrMn-Nb interface nearly restores T_c to that of the single layer Nb, but H_c1 still remains suppressed. These results suggest that, in addition to proximity effect and magnetic impurity scattering, magnetostatic interaction also plays a role in suppressing superconductivity of Nb in IrMn/Nb bilayers. In addition to reduced T_c and H_c1, the IrMn layer also induces broadening in the transition temperature of Nb, which can be accounted for by a finite distribution of stray field from IrMn.