Shiroka T Casola F Glazkov V Zheludev A Prša K Ott HR Mesot J 2011 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. application/pdf https://sonar.ch/global/documents/154783 eng info:eu-repo/semantics/altIdentifier/doi/10.1103/PhysRevLett.106.137202 info:eu-repo/semantics/altIdentifier/pmid/21517418 info:eu-repo/semantics/openAccess Physical review letters. - 2011 Distribution of NMR relaxations in a random Heisenberg chain. http://purl.org/coar/resource_type/c_6501