Detecting Rashba fields at the interface between Co and Si oxide by ferromagnetic resonance

Abstract

We report ferromagnetic resonance (FMR) experiments on thin magnetic Co layers either sandwiched symmetrically between Cu and Pt, or sandwiched asymmetrically between a Cu or Pt layer on one side and a ${\mathrm{SiO}}_{x}$ substrate on the other. In the symmetric samples, we find well-known behavior, namely, the FMR linewidth $\ensuremath{\Delta}{H}_{pp}$ is significantly larger for the case of Pt than for the case of Cu. This is due to the larger spin scattering in the Pt layer. However, for the asymmetric Co/Cu bilayers, the linewidth is much larger than for the symmetric Cu/Co/Cu trilayers and not much different from the linewidth of Co/Pt bilayers. We argue this to be due to the Rashba effect at the ${\mathrm{SiO}}_{x}/\mathrm{Co}$ interface, which gives rise to effective magnetic fields interacting with the electron spins in the Co layer and which can be measured without reverting to transport measurements.