Spin-lattice relaxation due to sliding of the modulation wave in incommensurate systems with impurities

Abstract

A theory of spin-lattice relaxation via large-scale fluctuations of the modulation wave in incommensurate systems is developed for the case of impurity pinning. For a simple model used for the description of such fluctuations, the motionally averaged spectrum and the positional dependence of ${\mathit{T}}_{1}$ in the slow-motion regime are calculated and illustrated graphically. In the thermally depinned regime close to the paraelectric-incommensurate transition temperature ${\mathit{T}}_{\mathit{I}}$, an anomalous temperature and Larmor-frequency dependence of the spin-lattice relaxation rate ${\mathit{T}}_{1}^{\mathrm{\ensuremath{-}}1}$ is predicted. It is shown that, on crossing ${\mathit{T}}_{\mathit{I}}$ from above, ${\mathit{T}}_{1}$ continues to decrease with decreasing temperature until it reaches a shallow minimum in the thermally depinned incommensurate phase.