SPIN-WAVE BRILLOUIN STUDY OF ULTRA-THIN CO AU(111) FILMS WITH PERPENDICULAR MAGNETIC-ANISOTROPY/

We have studied ultra-thin Co/Au(111) films with perpendicular magneti c anisotropy by means of spin-wave Brillouin scattering. The ultra-thi n Co films with thicknesses from 1 to 7 monolayer (ML) were grown by m olecular beam epitaxy on 1 ML Au underlayers without intentional subst rate heating. With 2 or more MLs of Co, spin-wave excitations are clea rly observed. We find the magnetic field dependence of the spin-wave e nergy can be quantitatively explained by a calculation including out-o f-plane magnetization due to uniaxial perpendicular magnetic anisotrop y. The first-order perpendicular anisotropy constant systematically in creases as the Ca thickness decreases from 7 to 3 ML. The second-order perpendicular anisotropy constant is much smaller than that expected in Co(0001) bulk and also increases as the Co thickness decreases. The physical origin of the thickness dependence of the perpendicular anis otropy is discussed. We find the field dependence of the scattering in tensity is different between Stokes and anti-Stokes processes; Finally , with 2 ML of Co, significant broadening of the spin-wave spectrum is observed, as well as the degradation of the perpendicular anisotropy. We believe this is the result of the effect of magnetic inhomogeneiti es due to the structural imperfections. (C) 1997 American Institute of Physics.