Electron paramagnetic resonance studies of Co2+ ions in congruent and nearly stoichiometric LiNbO3 single crystals

Congruent and nearly stoichiometric LiNbO3 single crystals doped with Co2ions have been investigated by the electron paramagnetic resonance techniqu e. The spin-Hamiltonian parameters, g(parallel to) = 2.671(2), g(perpendicu lar to) = 5.052(2), A(parallel to) = 40(2) x 10(-4) cm(-1), and A(perpendic ular to) = 154(1) x 10-4 cm(-1), are obtained without including the nuclear Zeeman and quadrupole interactions. The factor, k, of reduction due to the covalency is estimated as 0.92 less than or equal to k less than or equal to 1 using the above g-values. On the basis of the temperature dependence o f the linewidth, the spin-lattice relaxation and the spin-spin relaxation m echanisms are investigated. The former is a sum of a weak direct process wi th a phonon bottleneck (,similar to T-2.4),and,an Orbach process with Delta similar to 156 cm-1 (or 225 K), and the latter is a sum of a typical tempe rature-independent process and an anomalous process with a temperature depe ndence alpha T-3.6. This anomaly is considered as a shortening of T-2 due t o the increase of the correlation length of the spin-spin interaction as th e temperature decreases. The integrated signal intensity also showing an an omaly is a consequence of the linewidth anomaly.