Abstract

Abstract Chlorine NQR spin-lattice relaxation times T1Q were determined for [Co(H2O)6][PtCl6] at 4.2 400 K. Above ca. 350 K, T1Q decreased rapidly showing the onset of a reorientation of [PtCl6]2-. The activation energy Ea of this reorientation was determined as 125 ± 15 kJ mol-1. With decreasing temperature, T1Q showed a maximum at ca. 250 K. Below ca. 200 K, T1Q. is governed by the magnetic dipolar interaction between chlorines and paramagnetic Co2+ ions and is inversely proportional to the electron spin correlation time τe of CO2+ . τe is shown to be determined by the electron spin-lattice relaxation time T1e and the temperature independent correlation time rs for the spin-exchange between neighbouring ions above and below ca. 50 K, respectively. The temperature dependence of T1e is explained by assuming the Orbach process with an energy gap A/k of 530 + 20 K as T1e = 5 x 10-14 exp(530/T)s. τs was estimated to be 0.9 x 10-10 s. The temperature dependence of the ESR linewidth of Mn2+ impurities in single crystal was also measured, intending to study Co2+ spin dynamics. The limit of the ESR method is discussed by comparing the obtained results with those of the NQR method

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