Effect of antiferromagnet on superconductivity has been investigated in IrMn/Nb bilayers. Significant suppression of both transition temperature (Tc) and lower critical field (Hc1) 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 Tc to that of the single layer Nb, but Hc1 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 Tc and Hc1, 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.

We use lateral superconductor (SC)-ferromagnet (FM)-SC device to probe the magnetization reversal process of micron sized FM disk. Upon decreasing external magnetic field from saturated state, a buckling pattern forms first. The onset of buckling pattern and its switching to vortex state are studied with the help of Andreev conductance of the SC-FM interface below the critical temperature (Tc) of SC and the magnetoresistances both below and above the Tc. In the latter case, micromagnetic modeling has been carried out to interpret the experimental results by taking into account the current distributions when the electrodes are at different states.