NMR relaxation study of disorder in condensed matter - low temperature studies in the mixed system - $BPI_{1-x}BP_x$ - transition from classical to quantum rotation

Ramanuja, MN and Ramesh, KP and Ramakrishna, J (2008) NMR relaxation study of disorder in condensed matter - low temperature studies in the mixed system - $BPI_{1-x}BP_x$ - transition from classical to quantum rotation. In: Molecular Physics, 106 (6). pp. 745-751.

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Abstract

$^1H$ NMR spin-lattice relaxation time $(T_1)$ studies have been carried out in the mixed system, betaine phosphite–betaine phosphate $(BPI_{1-x}BP_x)$, to study the effects of disorder. The $T_1$ data in the temperature range 100K to 4K, at two Larmor frequencies 11.4 and 23.3 MHz, has been analysed following Lourens’ model, which shows a gradual transition from classical reorientations to quantum tunnelling motions. At lower temperatures, (when thermal motions become too slow) differences (due to disorder) in the local environments of the reorienting groups result in a distribution in the activation energy $(E_a)$ and the energy gap of the ground to the first excited torsional level $(E_{01})$. Below 50 K, the system moves into the quantum tunneling regime and the magnetization recovery shows biexponential behaviour which is another signature of disorder. These results are compared with those of the parent compounds BP and BPI.

Item Type:	Journal Article
Publication:	Molecular Physics
Publisher:	Taylor & Francis
Additional Information:	Copyright of this article belongs to Taylor & Francis.
Keywords:	NMR relaxation;disorder;mixed system;betaine phosphate (BP);betaine phosphite (BPI);protonglass;quantum tunneling;biexponential relaxation;activation energy distribution.
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	21 Jul 2008
Last Modified:	19 Sep 2010 04:47
URI:	http://eprints.iisc.ac.in/id/eprint/15179

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