Dynamics of negatively charged divacancies in neutron irradiated type Ib diamond

Abstract Thermal neutron irradiation of synthetic type Ib diamond, followed by annealing, results in a number of paramagnetic point defect centers. One of these is the composite defect designated W 29. Previous EPR measurements have shown that the W 29 center ( S  = 3/2) is a charged divacancy [ VV ] − with spin Hamiltonian parameters similar to those of the R 4/ W 6 neutral divacancy center [ VV ] 0 ( S  = 1) found in irradiated high purity type IIa diamond. The present EPR linewidth and spin-lattice relaxation rate measurements, made as a function of temperature on the W 29 center, show that an Orbach two-phonon process, with a gap of ~ 20 meV, plays a dominant role in determining the relaxation behavior above 20 K. Below 20 K a direct single phonon process provides the spin-lattice relaxation mechanism and the relaxation times become long, of the order of milliseconds. The linewidth behavior with temperature is accounted for in terms of changes in the spin dynamics.