Spin-lattice relaxation of the nuclear dipolar energy and spin diffusion in NH 4ClO 4

Abstract

The spin-lattice relaxation time of the dipolar energy T 1D and the characteristic time T SD for the spin diffusion between NH 4 + ions of different librational symmetry species were measured as functions of temperature and crystal orientation in NH 4ClO 4. T 1D shows shoulders around 44 and 28 K related to the librational tunnelling frequency and the proton resonance frequency, respectively. A broad minimum around 10 K corresponds to the linewidth transition. T SD is less than 0.5 ms above 4 K, showing that the ammonium protons in different symmetry species have, at least locally, a common spin temperature during the magnetization recovery.