Manipulation of Ferromagnetic domain by the terahertz free electron laser excitation

We performed ferromagnetic domain control in Erbium orthoferrite by excitation of the terahertz free electron laser. The magnetic domain structure, which was monitored by faraday microscopy, changes permanently by the irradiation of high-intensity terahertz pulses near the domain edges. The mechanism of the change of the magnetic domain structure was discussed and explained by the combination of the depinning effect and the entropic force induced by the excitation.