Brillouin-scattering studies of polycrystalline and amorphous sputtered films of Fe1−xBx and Co1−xBx

Abstract

We report on Brillouin‐scattering measurements of thermally excited acoustic‐surface phonons, and bulk and surface magnons, in sputtered films of Fe_1−xB_x and Co_1−xB_x. From the slope of the surface‐magnon frequency shift with field we determine g factors of 2.09±0.03 for Fe_1−xB_x and 2.16±0.03 for Co_1−xB_x, with no significant trend as a function of composition and no difference between amorphous and polycrystalline materials. The magnetization for pure Fe and Co agree with literature values. The magnetization of sputtered and quenched materials of the same composition are in agreement provided both samples are amorphous. Effective exchange corrections of order Dk²=0.1–0.5 kOe (where D is the spin‐wave stiffness and k is a magnon‐wave vector) are needed to properly fit the dependence of bulk‐magnon frequency shift on field. The magnetization values determined with such fits agree within experimental error with magnetizations obtained from the surface magnons. Possible origins of the Dk² correction are discussed. In films below about 200 nm in thickness, structure is observed in the bulk‐magnon peaks which may be due to standing spin waves. The potential of Brillouin scattering as a tool for thin‐film characterization is discussed.