Nonlinear magnetization dynamics of antiferromagnetic spin resonance induced by intense terahertz magnetic field

We report on the nonlinear magnetization dynamics of a HoFeO 3 crystal induced by a strong terahertz magnetic field resonantly enhanced with a split ring resonator and measured with magneto-optical Kerr effect microscopy. The terahertz magnetic field induces a large change (∼40%) in the spontaneous magnetization. The frequency of the antiferromagnetic resonance decreases in proportion to the square of the magnetization change. A modified Landau–Lifshitz–Gilbert equation with a phenomenological nonlinear damping term quantitatively reproduced the nonlinear dynamics.