FeSi diffusion barriers in Fe/FeSi/Si/FeSi/Fe multilayers and oscillatory antiferromagnetic exchange coupling

We study the diffusion of (57)Fe probe atoms in Fe/FeSi/Si/FeSi/Fe multilayers on Si(111) prepared by molecular beam epitaxy by means of (57)Fe conversion electron Mossbauer spectroscopy (CEMS). We demonstrate that the application of FeSi boundary layers successfully inhibits the diffusion of (57)Fe 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 angstrom, which was confirmed by the evolution of the isomer shift delta of the crucial CEM subspectrum. The formation of the slightly defective c-FeSi phase for thicker FeSi boundary layers (similar to 20 angstrom) was confirmed by CEMS and reflection high-energy electron diffraction (RHEED). Ferromagnetic resonance (FMR) shows that, for t(FeSi) = 0-14 angstrom, 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 similar to 6 angstrom.