Critical dynamics in layer-structured (${\mathrm{C}}_{18}$${\mathrm{H}}_{37}$${\mathrm{NH}}_3$${)}_2$${\mathrm{SnCl}}_6$

Phase transitions in the layer structured (${\mathrm{C}}_{18}$ ${\mathrm{H}}_{37}$ ${\mathrm{NH}}_3$ ${)}_2$ ${\mathrm{SnCl}}_6$ were studied by 200-MHz ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ NMR spin-lattice relaxation measurements. An order parameter corresponding to the order-disorder motion, defined by the fraction of the longer spin-lattice relaxation time constant component, revealed its three dimensionality, which was consistent with the temperature dependence of the spin-lattice relaxation rate. © 1996 The American Physical Society.