Raman process studied by Rb-87 spin-lattice relaxation in a Rb2ZnCl4 single crystal at low temperature

Rb-87 1/2 <----> 1/2 spin-lattice relaxation time in the Rb2ZnCl4 single cr ystal was measured in the temperature range of 4.2-300 K. The dominant rela xation of this crystal in the whole temperature range investigated here is due to quadrupolar interaction. The changes in the 87Rb spin-lattice relaxa tion rate near 75 and 192 K correspond to the phase transitions in the crys tal. These suggest that the phase IV to m transition is of second-order, an d the phase III to II transition is of first-order. The temperature depende nce of the relaxation rates in phases II, III, and TV is in accordance with the Raman process dominated by the phonon mechanism. (C) 2001 Published by Elsevier Science Ltd.