Brillouin light scattering study in ferromagnetically coupled Cu/Fe(110)/Cu/Fe(110)/Cu/Si(111) heterostructure: bilinear exchange magnetic couplings

Epitaxial Cu(60 Å)/Fe(20 Å)/Cu(dCu)/Fe(60 Å)/Cu(60 Å) heterostructures with the Cu spacer thickness dCu ranging between 0 and 33 Å have been grown on 737 reconstructed surface of Si~111! substrates. Fcc~111! Fe films grow epitaxially on the Cu~111! buffer layer up to a thickness of 6-8 Å, while, for larger thicknesses, one observes the appearance of three-dimensional bcc Fe~110! domains in the Kurdjumov-Sachs orientation. Brillouin light scattering ~BLS! from thermally excited spin waves has been exploited in order to study the interlayer exchange coupling between the two Fe films at room temperature. The experimental spin-wave frequency dependence on the applied magnetic field is simulated using a simple model which includes first-order intrinsic volume and interface anisotropies and takes the bilinear exchange interaction between the two ferromagnetic layers into account. We have found that for thicknesses of the Cu spacer larger than 6 Å, the Brillouin spectrum consists of two spin-wave modes due to the Fe double layered structure which depends on the Cu-layer thickness. The coupling is found to be ferromagnetic for the whole range of Cu spacer thicknesses investigated. Using the magnetic parameters determined by the above analysis, we have carried out a detailed calculation of the BLS cross section assuming the dynamic magnetization to be constant across each magnetic film. A very good agreement between the calculated and the measured cross sections has been obtained.