Spin waves in ultrathin hexagonal cobalt films on W(110), Cu(111), and Au(111) surfaces

Spin wave spectra of ultrathin epitaxial cobalt films deposited on W(110), Cu(111), and Au(111) surfaces are studied in the wavevector regime between 0.1 A super(-1) and 0.7 A super(-1) using inelastic electron scattering with 6 meV energy resolution. Up to three different spin wave modes are resolved for wave vectors q sub(||) < 0.35 A super(-1). The modes are identified as the acoustic mode and standing modes with one and two nodes inside the film. The broader appearance of the spectra at higher wave vectors compared to films grown on W(110) and Cu(111) is quantitatively accounted for by disorder-induced kinematic broadening. Because of the granular growth on copper and gold primarily the spin wave spectrum of cobalt films on W(110) is amenable to quantitative theoretical analysis. Such an analysis is not available at present. We show however, that the dispersion curves are incompatible with the Heisenberg model as long as only a single, layer-independent exchange coupling constant is invoked.