Anisotropic manipulation of subterahertz spin waves by spin orbit torque in the antiferromagnetic orthoferrite

We theoretically and numerically elucidate the electrical control over spin waves in antiferromagnetic (AFM) orthoferrite with biaxial anisotropies and Dzyaloshinskii-Moriya interactions. In orthoferrites, a canted AFM manifests as a bifurcated spin wave dispersion relation with distinct high-frequency and low-frequency spin wave bands. By deriving an effective coupled pendulum model, we demonstrate that the two spin wave bands are intrinsically coupled, with the coupling strength significantly enhanced under strong spin–orbit torque (SOT). The efficiency of frequency control is found to be inversely proportional to the effective potential energy, which is determined by anisotropy and DM interaction energies. Utilizing a heterostructure comprised of platinum, ferromagnet, and a canted AFM, we demonstrate anisotropic control of spin-wave bands via spin currents with three-dimensional spin polarizations, encompassing both resonant and propagating wave modes. Moreover, leveraging the confined geometry, we explore the possibility of controlling spin waves within a spectral domain ranging from tens of gigahertz to sub-terahertz frequencies. The implications of our findings suggest the potential for developing a terahertz wave source with electrical tunability, thereby facilitating its incorporation into ultrafast, broadband, and wireless communication technologies.