Spin dynamic studies on (2,5-dimethyl-DCNQI)2 Li by pulsed ESR

Abstract

The electron spin relaxation rates T1e−1 and T2e−1 of the radical anion salt (2,5-dimethyl-DCNQI)2Li are measured temperature- and angular dependent, respectively, at ν = 9.8 GHz. The temperature dependence can be explained by a smooth transition from motional narrowing to spin exchange. A more pronounced transition at 60 K leads to spin pairing. With further decreasing temperature the correlation time of the spin motion becomes longer to reach at 35 K τ = ωL−1 = 10−10 s. Below that temperature T1e−1 becomes smaller than T2e−1 which increases: at 4.5 K T1e−1 is 0.67 μs−1 (T1e = 1500 ns) and T2e−1 = 15 μs−1 (T2e = 67 ns). In the temperature range 300 – 35 K T1e is shorter than T2e, which demands an anisotropic fluctuating field with a spectral density: J(ω = ωL) > J(ω = 0). The angular dependencies of T1e−1 and T2e−1 cannot be explained by the symmetry of dipolar spin-spin interaction along the DCNQI stacks and the anisotropy of the g-factor, solely. We have to assume contributions from adjacent stacks, as well.