Anisotropic magnetoelastic coupling and tunable nonreciprocity of higher-order shear-horizontal waves in antiferromagnetic waveguides

Antiferromagnets can host the nonreciprocal propagation of elastic waves in the high-frequency regime via magnetoelastic coupling, but the hybridization between spin waves and conventional elastic waves often suffers from severe energy leakage and longitudinal strain interference. Fortunately, high-order shear-horizontal (SH) plate waves possess strict transverse polarization and rich dispersion characteristics, which opens the way for precise low-loss magnetoelastic manipulation. Here, we theoretically investigate the magnetoelastic coupling and nonreciprocal phenomena between double-sublattice spin waves and high-order SH plate waves in both single-layer NiO and NiO/Pt bilayer waveguides. For the single-layer waveguide, calculations show that a rigorous parity selection rule governs the periodic hybridization, in which odd-order spin waves hybridize exclusively with even-order SH wave modes, and vice versa. By applying surface free-spin boundary conditions, the spin-wave coupling in the low-frequency branch is eliminated while the hybridization in the high-frequency branch is enhanced significantly. Moreover, a specific Néel vector arrangement can completely suppress the magnetoelastic coupling. Furthermore, by introducing a heavy-metal Pt layer, tunable nonreciprocal frequency shifts can be achieved at the hybridization gaps by varying the applied magnetic field and the orientation of the Néel vector. This nonreciprocity originates from the simultaneous breaking of space-time inversion symmetry, induced by the interfacial Dzyaloshinskii-Moriya interaction and weak ferromagnetism. These results have promising applications in the development of nonreciprocal circulators, as well as in high-frequency spin-wave excitation and acoustic isolation.