Spin dynamics of the triplet Cr4+ in the vicinity of energy level anti-crossing

EPR spectra of the triplet Cr4+ in Y2SiO5 were investigated. Rhombic symmetry of zero-field splitting leads to three electron spin terms TX, TY, and TZ in the absence of the external magnetic field. We have observed the magnetically induced anti-crossing of the terms. In the vicinity of energy level anti-crossing the linewidths and positions of the resonance lines depend on temperature, which is explained by the dynamic Jahn–Teller effect. The temperature dependence of spin relaxation rates is described by the direct spin–lattice relaxation process limited to electron–phonon interactions, where the phonon frequencies are close to the applied microwave frequency.