Spin-wave Brillouin scattering in quasimonatomic Co films

We have observed spin-wave Brillouin scattering in ultrathin Co/Au/Cu/Si(111) films with the Co thicknesses t(Co) down to one monolayer (ML). A graded Co-wedge sample with t(Co) = 0-7 ML was prepared on 1 ML of Au interlayer by molecular beam epitaxy, where the thickness was calibrated by determining the number of deposited atoms using Rutherford backscattering spectroscopy. Observations of the spin-wave Brillouin excitation show directly collective and ferromagnetic ordering at room temperature. The t(Co) dependence of uniaxial perpendicular anisotropy is obtained from the field dependence of the spin-wave frequency. In addition, we quantify magnetic inhomogeneities from the field dependence of the spectrum width. With t(Co) less than or equal to 2 ML, the perpendicular anisotropy shows a steep decrease with decreasing t(Co), as well the structure-related magnetic inhomogeneity significantly increasing. (C) 1999 American Institute of Physics. [S0021-8979(99)64608-4].