Antiferromagnets, capable of hosting terahertz (THz)-frequency spin waves, are promising candidates for ultrafast, low-dissipation information processing. However, the systematic control of spin modes in antiferromagnetic orthoferrites remains relatively scarce. Here, we demonstrate the emission and detection of narrowband sub-THz radiation from quasi-ferromagnetic (q-FM) and quasi-antiferromagnetic (q-AFM) modes in ErxTm1−xFeO3 (x = 0, 0.5, and 1) single crystals. By varying the angle θ between the incident THz magnetic field (HTHz) and the c-axis, we can selectively excite either the q-AFM or q-FM mode and modulate their amplitude and relaxation dynamics. Furthermore, we show that the resonant THz frequencies in b-cut crystals are remarkably robust, exhibiting dependence on temperature and external magnetic fields (HDC). We calculated the magnetic anisotropy constants based on the temperature dependence of the spin waves. Finally, we generate narrowband THz emission via the inverse magneto-refraction effect by optically exciting q-AFM spin resonances.
Zhao et al. (2026) studied this question.