Brillouin light scattering from spin waves in Co_100-xCr_x alloy films

Collective spin waves in Co_100-xCr_x alloy films (x = 0, 9.2, 15.7 and 35.2 in at%) of 300±5 angstroms in thickness have been studied by means of Brillouin light scattering (BLS) at room temperature in magnetic fields of up to 4.0 kOe. Except for the Co_64.8Cr_35.2 film, we observed scattering from spin waves and determined the spin wave stiffness constant D_B. We obtained a value of D_B = (3.47±0.35)×10^-9 Oe cm² (436±44 meV angstroms²) for pure Co. Although this value is in good agreement with recent BLS values, it is rather smaller than the value of 510 meV angstroms² obtained from neutron scattering. For the alloys, the D_B value at x = 15.7 is strongly reduced to approximately 1/4 of the value at x = 9.2, while the saturation magnetization decreases almost linearly as the Cr content increases. We discuss this D_B behavior in terms of the Cr segregation which takes a place for Cr contents above x to approximately 12.