Non-Hermitian Topological Magnonics

The ferromagnetic resonance of the thermal mode occurs with a mode of zero wave vector. When the wavelength is long or the wave vector is small, the long-range dipolar interaction controls the movement of magnetic moments. Surface spin waves are associated with these modes, which are localized to the two surfaces of the magnetic material. As the wavelengths decrease, the short-range exchange interaction becomes dominant, leading to spin waves with frequencies as high as several terahertz. This recent discovery suggests that magnons can be utilized for information transport and storage due to various advantages. For instance, there is no Joule heating when the magnet moves through the magnetic insulator.