  Suppression of superconductivity due to the proximity effect between a
superconductor and a ferromagnet can be partially alleviated when a Cooper pair
simultaneously samples different directions of the short-range exchange field.
The superconductor's critical temperature, TC, is therefore expected to
partially recover when the ferromagnet is in a multi-domain state, as opposed
to a single-domain state. Here, we discuss series of experiments performed with
ferromagnet(Pt/Co)/spacer(IrMn and Pt)/superconductor(NbN) heterostructures. By
tuning the various parameters in play, e.g., superconducting coherence
length-to-thicknesses ratio, and domain sizes, we obtained up to 10 percent
recovery of the superconducting critical temperature {\Delta}TC/TC. This
large-scale recovery made novel investigations possible. In particular, from
the spacer thickness-dependence of {\Delta}TC/TC, it was possible to deduce the
characteristic length for Cooper pair penetration in an IrMn antiferromagnet.
This information is crucial for electronic transport, and up to now has been
difficult to access experimentally for antiferromagnets.
