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1H NMR study of molecular dynamics and phase transition in (NH4)2ZnBr4

Ramesha, KP and Devaraj, N and Ramakrishna, J and Vijayaraghavan, D (1992) 1H NMR study of molecular dynamics and phase transition in (NH4)2ZnBr4. In: Phase Transitions: A Multinational Journal, 37 (2-3). pp. 203-210.

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Abstract

The proton second moment (M2) and spin-lattice relaxation time (T1) have been measured in (NH4)2ZnBr4 in the range 77-300 K. The room-temperature spectrum shows a structure which disappears around 243 K. The signal is strong and narrow even at 77 K. Proton T1 shows a maximum at 263 K, caused by spin rotation interaction and decreases with decreasing temperature till 235 K, where it shows a sudden increase. Below 235 K, again it decreases and shows a slope change around 216.5 K (reported Tc). From 216.5 K, T1 decreases continuously without exhibiting any minimum down to 77 K. The narrow line at 77 K, and absence of a T1 minimum down to 77 K indicate the possibility of quantum mechanical tunnelling in this system. Motional parameters such as activation energy and pre-exponential factor have been evaluated for the reorientational motion of the NH+4 ion.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Taylor and Francis Group.
Keywords: Second moment;spin-lattice relaxation time;activation energy; spin-rotation interaction;phase transition;reorientation.
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 01 Apr 2011 09:18
Last Modified: 22 Nov 2011 06:52
URI: http://eprints.iisc.ernet.in/id/eprint/36151

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