  We investigated the influence of doping antiferromagnetic MnN in
polycrystalline MnN/CoFe exchange bias systems, showing high exchange bias of
up to 1800 Oe at room temperature. The thermal stability of those systems is
limited by nitrogen diffusion that occurs during annealing processes. In order
to improve the thermal stability, defect energies of elements throughout the
periodic table substituting Mn were calculated via density functional theory.
Elements calculated to have negative defect energies bind nitrogen stronger to
the lattice and could be able to prevent diffusion. We prepared exchange bias
stacks with doping concentrations of a few percent by (reactive) co-sputtering,
testing doping elements with defect energies ranging from highly negative to
slightly positive. We show that doping with elements calculated to have
negative defect energies indeed improves the thermal stability. Y doped MnN
layers with doping concentrations below 2% result in systems that show exchange
bias fields higher than 1000 Oe for annealing temperatures up to 485{\deg} C.
