Brillouin light-scattering study of TbFeCo thin films

Abstract

Spin-wave excitations have been observed, using Brillouin light scattering, in thin films of TbFeCo, grown by sputtering on silicon substrates, with thicknesses in the range 4.5–250 nm. The variations of spin-wave frequency with applied in-plane magnetic-field H (100 Oe⩽H⩽4.5 kOe) and in-plane magnon wave-number k (4.24×104⩽k⩽2.41×105 cm−1) were obtained. For these films, oxidation during the deposition process produces a bulk film, which is very weakly ferrimagnetic and, therefore, largely magnetically dead. However, further oxidation, at the film surface after deposition, due to exposure to air, increases the magnetization to produce a magnetically active surface layer. The results were modeled as a Damon–Eshbach surface mode, and the TbFeCo films considered as a magnetic film on a nonmagnetic layer, the thicknesses of which were both unknown. The frequency versus field measurements enabled values for the saturation magnetization and gyromagnetic ratio to be determined. The measurements of the frequency versus wave number showed evidence that, for the thicker films, the magnetically active layer was only a small fraction of the total thickness, and the active layer thicknesses were determined. The values of magnetizations are compared with those obtained from vibrating sample magnetometry measurements.