Room-temperature electron spin dynamics of Ce³⁺ ions in a YAG crystal

Circularly polarized optical excitation generates electron spin polarization in the lowest 5d state of rare-earth Ce³⁺ ions in a YAG crystal. The 5d electron spin dynamics is investigated in transverse and longitudinal magnetic fields by time-resolved pump-probe Faraday rotation. Long lived electron spin coherence with a dephasing time of 2.5 ns is found at room temperature. In a transverse magnetic field of 1 T, the electron spin coherence shows a distinct beating-like amplitude modulation due to several slightly different Larmor frequencies corresponding to different electron g factors of magnetically inequivalent positions of the Ce³⁺ ions in the crystal lattice. Hyperfine coupling between the 5d electron of Ce³⁺ ions and environmental nuclear spins dominates the spin relaxation, which can be efficiently suppressed by a longitudinal magnetic field as small as 10 mT. The dependence of electron spin relaxation on both the transverse and longitudinal magnetic fields agrees well with the one predicted theoretically for the hyperfine coupling mechanism.