In situ Brillouin light scattering from ultrathin epitaxial Fe/Ag(100) films with Cr and Ag overlayers

Abstract

We have studied the magnetic properties of ultrathin epitaxial Fe/Ag(100) films by means of in situ Brillouin light scattering (BLS) in an ultrahigh vacuum chamber equipped with magneto-optic Kerr effect, low energy electron diffraction, and reflection high energy electron diffraction instruments. Our novel in situ BLS system allows us to perform measurements rapidly, in order to avoid surface contamination, and hence to observe the evolution of the spin-wave frequency with increasing film thickness. Good reproducibility is observed between different growth runs. The direction of the applied field within the film plane has been varied revealing that the magnetocrystalline anisotropy has cubic symmetry and that there is no observable in-plane uniaxial anisotropy. From the values of the hard and easy axis spin wave frequencies we have determined the values of the in-plane fourfold anisotropy and effective demagnetizing fields during the growth of 13.9 monolayer (ML) Fe films. The evolution of the fourfold anisotropy is in reasonable agreement with that reported by other researchers. The effect of depositing Cr and Ag overlayers onto the completed 13.9 ML film has also been studied. We have deduced values for the surface anisotropy constants for the Fe/Ag and Fe/vacuum interfaces and we compare these with previously reported values. A qualitatively different evolution of the spin wave frequency with overlayer thickness is observed for the deposition of Cr and Ag, which may be related to the magnetic properties of the Cr overlayer.