Altermagnetism induces momentum-dependent splitting not only in electronic bands but also in magnon spectra. However, the unconventional chiral behavior of magnons in altermagnetic systems remains inadequately understood, limiting the development of novel spintronic functionalities. Here, we investigate the intrinsic altermagnetic magnon splitting in fourteen orthoferrites RFeO3 (R = rare earth) using first-principles calculations and spin Hamiltonian analysis. We demonstrate that the chiral magnon modes originate from non-relativistic, symmetry-breaking exchange interactions, which lead to distinct momentum-dependent splitting and generate a transverse spin current Lₗₙ. In the canted antiferromagnetic ground state of RFeO3, the magnon splitting due to relativistic Dzyaloshinskii–Moriya interaction (DMI) and the non-relativistic altermagnetic contribution coexist but interact weakly and largely independently. Furthermore, we propose a general strain-control mechanism, whereby anisotropic strain modifies the inequivalent superexchange paths through displacement of the rare-earth atoms. This mechanism enables tunable chiral magnon band splitting and spin current, thus making it possible to realize controllable dissipationless magnon current. Our results provide fundamental insights into altermagnetic magnonics and offer new strategies for dissipationless spintronic device.
Shen et al. (Mon,) studied this question.