[en] In the present work, we studied the effect of Ag doping on Fe self-diffusion in iron mononitride (FeN) thin films. FeN thin films were prepared with and without Ag doping using reactive nitrogen magnetron sputtering. Single phase FeN thin films with a marker layer of ⁵⁷FeXN (X=0, Ag) were deposited at 623 K and characterised using 104 x-ray diffraction (XRD), x-ray reflectivity (XRR), conversion electron Mössbauer spectroscopy (CEMS), soft x-ray absorption spectroscopy (SXAS) and neutron reflectivity (NR). Detailed measurements confirmed that films are single phase with a lattice parameter (LP) of about 4.3 Å nm even when doped with about 5 at% Ag. Self-diffusion measurements were carried out using secondary ion mass spectroscopy (SIMS) and it was found that over all diffusion lengths were smaller with Ag doping, however the variation of Fe self-diffusion with temperature remains similar to un-doped sample. Since in the mononitride composition, it is very difficult to control Fe diffusion, our results with a smaller doping of Ag are encouraging that it can be at least controlled to some extent. It is proposed that by tuning the Ag doping further control of Fe diffusion and hence the thermal stability of FeN can be enhanced. (author)