Spin-lattice relaxation of exchange-coupled Cu2+-Cu2+ pairs and single Cu2+ ions in crystals of zinc (II) bis(diethyl-dithiocarbamate)

Abstract

Detailed investigations of the spin-lattice relaxation of single Cu 2+ ions and Cu2+-Cu2+ pairs in zinc (II) bis(di- ethyl-dithiocarbamate) single crystals are reported. The measurements were made in the temperature range 1.5<T<35K at v=28.8 and 9.0 GHz using the pulse saturation and the spin-echo method, respectively. At T<5K the single-ion relaxation is defined by direct processes; at higher temperatures two-phonon Raman processes were observed. In the range 4<T<12K the data can be fitted by an Orbach-Aminov process. A calculation of the single-ion relaxation rate for the direct process has been made. Also the pair relaxation rate in the same range was calculated considering the rate equations of the populations of the triplet state. From the temperature dependence of the Orbach-Aminov process the isotropic exchange integral was derived. Low-temperature EPR measurements provided the signs of the D-tensor and of the exchange integral. From the temperature dependence of the single-ion Raman relaxation rate the Debye temperature of the host crystal was estimated. For exchange coupled pairs the anomalous frequency dependence of T1 -1 was observed.