We use microfocus Brillouin light scattering spectroscopy to study the effects of spin-orbit torque on thermal spin waves in almost angular momentum compensated ferrimagnetic $\mathrm{Co}$-$\mathrm{Gd}$ alloy films. The spin-orbit torque is produced by the electric current flowing in the $\mathrm{Pt}$ layer adjacent to the $\mathrm{Co}$-$\mathrm{Gd}$ film. Both the ferromagnetic and the exchange modes are detected in our measurements. The intensity and the linewidth of the ferromagnetic mode are modified by the spin-orbit torque. In contrast, the properties of the exchange mode are unaffected by the spin-orbit torque. We also find that the frequencies and the linewidths of both modes are significantly modified by Joule heating, owing to the strong temperature dependence of the magnetic properties of $\mathrm{Co}$-$\mathrm{Gd}$ in the vicinity of the angular momentum compensation point. Our results provide insight into the mechanisms that can enable the implementation of subterahertz magnetic nano-oscillators based on ferrimagnetic materials, as well as related effects in antiferromagnets.

• Received 23 June 2020
• Revised 31 August 2020
• Accepted 15 September 2020

DOI:https://doi.org/10.1103/PhysRevApplied.14.044016