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Low-energy excitations in the S=(1/2) molecular nanomagnet K6[V<sub>15</sub><sup>IV</sup>As6O42(H2O)]·8H2O from proton NMR and µSR

Procissi, D. and Lascialfari, A. and Micotti, E. and Bertassi, M. and Carretta, P. and Furukawa, Y. and Kögerler, P. (2006) Low-energy excitations in the S=(1/2) molecular nanomagnet K6[V<sub>15</sub><sup>IV</sup>As6O42(H2O)]·8H2O from proton NMR and µSR. Physical Review B, 73 (18). Art. No. 184417. ISSN 1098-0121. doi:10.1103/PhysRevB.73.184417.

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Zero- and longitudinal-field muon-spin-rotation (µSR) and 1H NMR measurements on the S=(1/2) molecular nanomagnet K6[V<sub>15</sub><sup>IV</sup>As6O42(H2O)]·8H2O are presented. In LF experiments, the muon asymmetry P(t) was fitted by the sum of three different exponential components with fixed weights. The different muon relaxation rates lambdai (i=1,2,3) and the low-field H=0.23 T 1H NMR spin-lattice relaxation rate 1/T1 show a similar behavior for T>50 K: starting from room temperature they increase as the temperature is decreased. The increase of lambdai and 1/T1 can be attributed to the "condensation" of the system toward the lowest-lying energy levels. The gap Delta~550 K between the first and second S=(3/2) excited states was determined experimentally. For T<2 K, the muon relaxation rates lambdai stay constant, independently of the field value H<=0.15 T. The behavior for T<2 K strongly suggests that, at low T, the spin fluctuations are not thermally driven but rather originate from quasielastic intramolecular or intermolecular magnetic interactions. We suggest that the very-low-temperature relaxation rates could be driven by energy exchanges between two almost degenerate S=(1/2) ground states and/or by quantum effects.

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Additional Information:©2006 The American Physical Society (Received 22 March 2006; published 15 May 2006) F. Pratt is gratefully acknowledged for help in the experimental µSR measurements. One of the authors (Y.P.) thanks the 21 Century COE Programs “Topological Science and Technology” at Hokkaido University and the Sumitomo Foundation for financial support. This work was supported by FIRB project RBNE01YLKN-2001, RTB Quemolna, and NoE MAGMANET.
Subject Keywords:potassium compounds; molecular magnetism; nanostructured materials; proton magnetic resonance; muon probes; nuclear spin-lattice relaxation; ground states; excited states
Issue or Number:18
Record Number:CaltechAUTHORS:PROprb06
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4628
Deposited By: Archive Administrator
Deposited On:30 Aug 2006
Last Modified:08 Nov 2021 20:18

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