Low-temperature time-domain terahertz spectroscopy of terbium gallium garnet crystals

We report an experimental observation of high frequency magnetic excitations in terbium gallium garnet crystals using terahertz time-domain spectroscopy. We show that precessional modes of terbium magnetic sublattices can be excited by a magnetic field of a terahertz broadband pulse. We study and discuss the dependence of the observed resonances upon the temperature and the strength and orientation of the bias magnetic field. The behavior of the observed magnetic modes is in agreement with the theory of paramagnetic resonance in the multisublattice system. We also show that the illumination of the crystal with intense optical pulses destroys the magnetic ordering. Our results demonstrate that the time-domain terahertz spectroscopy can be a powerful tool by which to study high frequency properties of dielectric magnetic materials, with perceived extensions to studies in femtomagnetism and magnonics. DOI: 10.1103/PhysRevB.87.094414