Ultrafast Magnon Dynamics in Antiferromagnetic Nickel Oxide Observed by Optical Pump-Probe and Terahertz Time-Domain Spectroscopies

We have studied the ultrafast magnon dynamics in an antiferromagnetic 3d-transition-metal monoxide, nickel oxide (NiO), using optical pump-probe spectroscopy and terahertz time-domain spectroscopy (THz- TDS). Terahertz damped magnon oscillations were observed in the Faraday rotation signal and in the transmitted THz electric field via optical pump-probe spectroscopy and THz-TDS, respectively. Three magnon modes were observed via optical pump-probe spectroscopy, and two magnon modes were observed via THz-TDS. The observed temperature dependence of the magnon frequencies is discussed using three different molecular field theories.