  Exchange coupling between two magnetic layers through an interlayer is of
broad interest for numerous recent applications of nano-magnetic systems. In
this Letter we study ferromagnetic exchange coupling through amorphous
paramagnetic Fe-Ta alloys. We show that the exchange coupling depends
exponentially on spacer thickness and scales with the Fe-Ta susceptibility,
which can be tuned via the alloy composition and/or temperature. Such materials
are of high interest for the engineering of perpendicularly magnetized
CoFeB-MgO based tunnel junctions as it enables ferromagnetic coupling of
magnetic layers with differing crystalline lattices, suppresses dead layers and
can act as an inter-diffusion barrier during annealing.
