Brillouin light scattering studies of iron-cobalt multilayers

Spin wave excitations have been observed in a series of sputtered iron-cobalt (FeCo) multilayer structures using Brillouin light scattering. The substrate in all cases was GaAs (001) and the total FeCo thickness was maintained at a nominal 170 nm; non-magnetic spacer layers of Ag and Cu with nominal thicknesses of 2 nm and an amorphous magnetic FeSiBC layer of 4 nm thickness were used. The saturation inductions B_s were found to be in the range of 1.5-2.1 T, i.e. smaller than the bulk value of 2.44 T. The disparity between the bulk and multilayer values is attributed to microstructural features which suggest that the multilayers are stacks of bilayers consisting of a film with bulk-like properties in contact with a 'composite' film with a smaller magnetisation. Each bilayer can then be treated as a single layer with a volume-averaged magnetisation. In general the multilayer structures showed no observable uniaxial anisotropy and any cubic anisotropy fields were of a small magnitude ∼ 0.03 T. The results illustrate the use of Brillouin light scattering as a diagnostic tool in inhomogeneous systems.