Relaxation study of a 3d5 ion in Td symmetry : Mn+ + in Zns

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Abstract
The relaxation behaviour of Mn2+ in cubic ZnS has been studied between 1.3 and 135 K, at 9.3 GHz, with a pulse saturation method. At low temperatures, the variation of the recovery signal with the saturating pulse duration indicates that the system acquires a spin-temperature before relaxing. The diffusion process maintaining the spin-temperature is temperature independent and has a time constant TD = 0.5 ms. Complementary studies using a fast field sweep technique confirm that the whole system of 30 EPR lines acquires a spin temperature. When T < 10 K, relaxation takes place via a direct process, and T1 T = 1.18 Ks. When T1 > 10 K, we observe a Raman process (1/T1 ∝ T I 6 (168/T)). In the case of the direct process, relaxation is well described by a dynamic hamiltonian deduced from uniaxial stress measurements. A determination of the Raman contribution to relaxation made with Van Vleck's normal mode formalism leads to a T1 value which is an order of magnitude greater than the experimental value. In both cases tranverse phonons are the most efficient