Ultrafast Spin Dynamics in the Iron Borate Easy-Plane Weak Ferromagnet

Ultrafast processes of the spin dynamics in iron borate FeBO 3 are considered theoretically; the mechanisms responsible for excitation of quasi-ferromagnetic as well as quasi-antiferromagnetic spin resonance modes by a one-period terahertz pulse are indicated. In full agreement with experimental observations [27], the excitation of the high-frequency quasi-antiferromagnetic mode is resonant by nature, and its amplitude is a linear function of the electric field of the terahertz pulse. The amplitude of the low-frequency quasi-ferromagnetic mode is a quadratic function of the electric field of the pulse, and the excitation of this mode is governed by the mechanism of the inverse Cotton–Mouton effect.