Crosstalk and Oersted Field Interference Resolve the Hidden Spin-Wave Puzzle in Hematite.

A recent study reporting interferencelike patterns in nonlocal spin-wave measurements on hematite [Sheng et al., Control of spin currents by magnon interference in a canted antiferromagnet, Nat. Phys. 21, 740 (2025).NPAHAX1745-247310.1038/s41567-025-02819-7] suggested the existence of a hidden ultrafast spin-wave mode at tens of gigahertz. This hidden mode lies beyond the scope of conventional spin-wave theory in hematite, and its origin remains unexplained. In this Letter, we show that two mechanisms-crosstalk-induced spin-orbit torque and the antenna-generated Oersted field-quantitatively account for all observed interferencelike features, eliminating the need for a hypothetical hidden mode. We find that the spin-orbit torque generates both out-of-plane local magnetization dynamics and in-plane polarized propagating spin waves. While the former, combined with the antenna-generated propagating spin waves, leads to a frequency-dependent sign in the detected spin pumping signal, the latter gives rise to a finite Brillouin light scattering signal at twice the microwave frequency. Meanwhile, the Oersted field, which possesses both in-plane and out-of-plane components, produces the spatial oscillation profile previously observed in Brillouin light scattering at the excitation frequency. Such a spatial modulation is found to persist even in the absence of the crosstalk-induced spin-orbit torque, indicating that it arises from a conventional excitation effect. Our results not only elucidate the roles of spin-orbit torque and Oersted field in the magnetization dynamics of easy-plane antiferromagnets but also highlight the significance of crosstalk effects in nonlocal spin-wave measurements using microwave excitation and heavy-metal detectors.