Signatures of a bath of altermagnetic magnons on ferromagnetic spin waves

The effects of altermagnets (AMs) on other layers within heterostructures containing magnetic materials are much less well understood than those of regular antiferromagnets (AFs). The latter perform critical functions in spintronic devices, such as pinning the magnetization of ferromagnetic (FM) layers, and their high excitation frequency is desirable in magnonic applications. As such, the distinctive properties of AMs are envisaged to provide additional knobs to control magnetization dynamics. In this talk, we study the propagation of classical spin waves within a FM underneath a layer of an insulating AM, whose quantum magnons act as a dissipative bath. Using Schwinger-Keldysh field theory, we derive an extended Landau-Lifshitz equation governing the dynamics of the localized FM spins, with modified anisotropy and exchange couplings, as well as nonlocal and direction-dependent damping. Consequently, the resulting FM spin-wave spectrum contains signatures that reveal the altermagnetic order of the overlayer and may be used to test candidate materials. Conversely, AMs within such bilayers may provide a means of engineering and controlling dissipation in spintronic and magnonic devices.