Using monolayers of argon physisorbed on in-plane magnetized thin cobalt films, we demonstrate that spin selective core-hole-clock measurements become possible by spin filtering the decay electrons, even if spin selective excitation of the core resonance is excluded. We foresee a wide range of applications for this approach to spin selective investigations of electron transfer dynamics, in particular for organics in contact with ferromagnetic materials as in systems of molecular spintronics. (C) 2015 Elsevier B.V. All rights reserved.