Terahertz nonlinear magnetic response in antiferromagnets

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. The terahertz magnetic field induces a large magnetization change of 40% of the spontaneous magnetization. The frequency of the antiferromagnetic resonance decreases in proportion to the square of the magnetization change.