Spin-lattice relaxation: Non-Bloembergen-Purcell-Pound behavior by structural disorder and Coulomb interactions

We study, by Monte Carlo simulation, the spin lattice relaxation rate 1/${\mathit{T}}_1$(ω,T) caused by diffusing ions in disordered structures. We show that both disorder and Coulomb interactions are essential to obtain the typical non-Bloembergen-Purcell-Pound behavior of 1/${\mathit{T}}_1$. The dependence of 1/${\mathit{T}}_1$ upon frequency ω and temperature T can be described by the simple scaling form 1/${\mathit{T}}_1$=${\mathrm{\omega }}^{\mathrm{-}1}$f(ωτ). We find that the NMR correlation time τ is more highly activated than the conductivity relaxation time ${\mathrm{\tau }}_{\mathrm{\sigma }}$, which is in agreement with very recent experimental results.