We study the diffusion of ⁵⁷Fe probe atoms in Fe/FeSi/Si/FeSi/Fe multilayers on Si(111) prepared by molecular beam epitaxy by means of ⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS). We demonstrate that the application of FeSi boundary layers successfully inhibits the diffusion of ⁵⁷Fe into the Si layer. The critical thickness for the complete prevention of Fe diffusion takes place at a nominal FeSi thickness of t_FeSi = 10-12 Å, which was confirmed by the evolution of the isomer shift δ of the crucial CEM subspectrum. The formation of the slightly defective c-FeSi phase for thicker FeSi boundary layers ( ∼ 20 Å) was confirmed by CEMS and reflection high-energy electron diffraction (RHEED). Ferromagnetic resonance (FMR) shows that, for t_FeSi = 0-14 Å, the Fe layers in all samples are antiferromagnetically coupled and we observe an oscillatory antiferromagnetic coupling strength with FMR and superconducting quantum interference device (SQUID) magnetometry for varying FeSi thickness with a period of  ∼ 6 Å.