The temperature dependence of the energy of ferromagnetic spin waves in an epitaxially grown 300-Å [0001] Gd film is shown to depend on the bulk values of the c-axis magnetic-stiffness constant ${\mathit{D}}_{\mathit{c}}$, defined by ω(q)=${\mathit{tsum}}_{\mathit{i}}$${\mathit{D}}_{\mathit{i}}$${\mathit{q}}_{\mathit{i}}^2$, where ‖qa‖≪1, and the axial-anisotropy constant ${\mathit{P}}_2$, defined by ${\mathit{scrH}}_{\mathrm{aniso}}$ =${\mathit{P}}_2$ (${\mathit{S}}_{\mathit{z}}$${)}^2$+.... Two bulk spin waves and one Damon-Eshbach surface magnetostatic wave were probed with Brillouin light scattering. The bulk spin waves were found to be sensitive to the exchange interaction. In contrast, the Damon-Eshbach surface magnetostatic wave, although insensitive to the exchange interaction, is influenced noticeably by the axial magnetic anisotropy ${\mathit{P}}_2$(T) present in Gd. Ignoring surface anisotropy, we extracted values of ${\mathit{D}}_{\mathit{c}}$(T) and ${\mathit{P}}_2$(T) from the Brillouin data and from the magnetization of the Gd film determined by a superconducting-quantum-interference-device magnetometer. Within the experimental errors, these values are reasonably consistent with the bulk values from the literature.

• Received 26 December 1991

DOI:https://doi.org/10.1103/PhysRevB.45.12297