Coupling of terahertz light with nanometre-wavelength magnon modes via spin-orbit torque

Engineering of the spin-orbit interactions in a magnetic multilayered structure makes it possible to coherently generate coherent spin waves using terahertz radiation, which could benefit the development of spintronic devices. Spin-based technologies can operate at terahertz frequencies but require manipulation techniques that work at ultrafast timescales to become practical. For instance, devices based on spin waves, also known as magnons, require efficient generation of high-energy exchange spin waves at nanometre wavelengths. To achieve this, a substantial coupling is needed between the magnon modes and an electro-magnetic stimulus such as a coherent terahertz field pulse. However, it has been difficult to excite non-uniform spin waves efficiently using terahertz light because of the large momentum mismatch between the submillimetre-wave radiation and the nanometre-sized spin waves. Here we improve the light-matter interaction by engineering thin films to exploit relativistic spin-orbit torques that are confined to the interfaces of heavy metal/ferromagnet heterostructures. We are able to excite spin-wave modes with frequencies of up to 0.6 THz and wavelengths as short as 6 nm using broadband terahertz radiation. Numerical simulations demonstrate that the coupling of terahertz light to exchange-dominated magnons originates solely from interfacial spin-orbit torques. Our results are of general applicability to other magnetic multilayered structures, and offer the prospect of nanoscale control of high-frequency signals.

Automated summary

Engineering of spin-orbit interactions in a magnetic multilayered structure enables the coherent generation of spin waves using terahertz radiation, benefiting spintronic device development. By exploiting relativistic spin-orbit torques confined to metal/ferromagnet interfaces, we improve light-matter interaction and successfully excite spin-wave modes with frequencies up to 0.6 THz and wavelengths as short as 6 nm using broadband terahertz radiation. Our results have broad applicability and offer the potential for nanoscale control of high-frequency signals.