“…Recently we have suggested a new application for hard magnetic insulators, namely, their utilization as media for generating a powerful spin current induced by sub-terahertz/terahertz radiation that can be used in ultrafast spintronics. 40,78,79 For faster electronics, it is necessary to increase the operating frequencies, for example, those of electronic resonances. Sufficiently high frequencies (sub-terahertz and terahertz ranges) are known for antiferromagnetic resonances.…”