Spin-wave modes and line broadening in strongly coupled epitaxial Fe/Al/Fe and Fe/Si/Fe trilayers observed by Brillouin light scattering

We report on the spin-wave excitation frequencies and the broadening of the mode linewidths in Stokes and anti-Stokes Brillouin light scattering spectra of strongly exchange coupled (2-6.5 mJ/m(2)), epitaxial trilayers with the following structures: Fe(80 Angstrom)/Si wedge/Fe(100 Angstrom) and Fe(50 Angstrom)/Al wedge/Fe(70 Angstrom). Both spacer materials yield qualitatively similar spectra which evolve in the same way when the spacer thickness increases. We determine the type of interlayer coupling and quantify its strength as a function of the spacer thickness by comparing and fitting the mode positions to a model calculation. Furthermore, we observe clearly different behaviors of the mode linewidths as a function of spacer thickness for the optic and acoustic modes. There are also strong differences between the Stokes and anti-Stokes side of the spectra. The largest linewidths of up to 8 GHz occur at spacer thicknesses between 5 and 8 Angstrom for both spacer materials. Lateral averaging and two-magnon scattering are qualitatively discussed as possible sources for the line-broadening. (C) 2003 American Institute of Physics