High-Frequency EPR Spectroscopy of Tb3+ Ions in Synthetic Forsterite

Paramagnetic centers formed by the impurity Tb³⁺ ions in synthetic forsterite Mg₂SiO₄ have been studied by high-frequency tunable electron paramagnetic resonance spectroscopy in the frequency range of 150–300 GHz. These centers represent single Tb³⁺ ions and dimer associates of the Tb³⁺ ions. It has been found that the integral intensity of resonance transitions belonging to the dimer centers is much higher than that to be expected for the statistical distribution of the impurity Tb ions in the forsterite host. Therefore, there is a mechanism favoring the self-organization of the Tb ions in dimer associates during the crystal growth. The parameters of the effective spin Hamiltonian describing the dependence of electron-nuclear sublevels on the magnetic field have been determined for all observed paramagnetic centers and the possible structures of the centers have been discussed.