Laser excitation of magnons in NiO via spin-phonon coupling

Antiferromagnetic materials have recently been proposed as new types of terahertz (THz) range spintronic devices owing to their ultrafast spin dynamics. Manipulating their spin dynamics expediently, however, remains a key challenge. Here, we demonstrate the laser excitation of magnons in a prototypical antiferromagnet NiO via spin-phonon coupling. The terahertz time-domain spectrum revealed the frequencies of antiferromagnetic magnons near 1 THz. Laser excitations in the visible spectrum caused a noticeable softening of the magnons. Raman spectroscopy results established the presence of optical phonons. The laser heating effect was excluded by finite-element analysis and variable-temperature measurements. The temperature- and power-dependent properties suggest an optical phonon-magnon coupling mechanism. Laser excitation raises the optical phonon temperature, linked with the magnon temperature, via the magnon-phonon interaction. Consequently, the magnon temperature rises, and the magnon mode frequency softens. Our findings shed light on spin-phonon coupling in antiferromagnetic insulators and open a route for creating rapid opto-spintronic devices that utilize antiferromagnetic materials.