Proton-spin—lattice relaxation in the antiferromagnetic state of CsMnCl3·2H2O

The spin-lattice relaxation times of protons in the nearly one-dimensional Heisenberg system CsMn${\mathrm{Cl}}_3$·2${\mathrm{H}}_2$O were measured between 1.1 and 3.9 K in the antiferromagnetic state. From the comparison of the ratio of the relaxation rates of two nonequivalent protons with the calculated ratio, it was concluded that the two-magnon process dominates at low temperatures and the exchange-enhanced three-magnon process at high temperatures. A quantitative calculation of these contributions, without the restriction of a small-$k$ approximation, based on the values for the exchange constants available in the literature, gives a fair agreement with the experimental results. The relaxation time is very sensitive to the interchain coupling and a fitting procedure to our experimental data yields an interchain coupling of (5±1)% of the intrachain coupling.