Distribution of NMR relaxations in a random Heisenberg chain |
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Authors: | Shiroka T Casola F Glazkov V Zheludev A Prša K Ott H-R Mesot J |
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Institution: | Laboratorium für Festk?rperphysik, ETH H?nggerberg, CH-8093 Zürich, Switzerland. |
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Abstract: | NMR measurements of the (29)Si spin-lattice relaxation time T(1) were used to probe the spin-1/2 random Heisenberg chain compound BaCu(2)(Si(1-x)Ge(x))(2)O(7). Remarkable differences between the pure (x=0) and the fully random (x=0.5) cases are observed, indicating that randomness generates a distribution of local magnetic relaxations. This distribution, which is reflected in a stretched exponential NMR relaxation, exhibits a progressive broadening with decreasing temperature, caused by a growing inequivalence of magnetic sites. Compelling independent evidence for the influence of randomness is also obtained from magnetization data and Monte Carlo calculations. These results suggest the formation of random-singlet states in this class of materials, as previously predicted by theory. |
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