Ultrafast time domain demonstration of bulk magnetization precession at zero magnetic field ferromagnetic resonance induced by terahertz magnetic field

We report the first observation of sub-terahertz bulk-magnetization precession, using terahertz time-domain spectroscopy. The magnetization precession in gallium-substituted e-iron oxide nano-ferromagnets under zero magnetic field is induced by the impulsive magnetic field of the THz wave through the gyromagnetic effect. Just at the resonance frequency, the linear to circular polarized wave conversion is realized. This is understood as the free induction decay signal radiated from a rotating magnetic dipole corresponding to the natural resonance. Furthermore, this demonstration reveals that the series of gallium-substituted e-iron oxide nano-ferromagnets is very prospective for magnetooptic devices, which work at room temperature without external magnetic field, in next-generation wireless communication. (C) 2010 Optical Society of America