Ultrafast Coherent Control of Spin Precession Motion by Terahertz Magnetic Pulses

We demonstrated coherent control of spin precession motion due to the ferromagnetic resonance induced by magnetic field component of ultrashort terahertz pulses. The amplitude of the precession can be controlled by the pulse separation time of the double pulse excitation technique. We succeeded in observing the energy transfer between spin and photon systems, and the energy of the spin system is returned to the second terahertz pulses instantaneously when the precession amplitude is cancelled.