Thermal conductivity of Cu1-xMgxGeO3

The T-dependence of the thermal conductivity is measured in a series of Cu1 - xMgxGeO3 crystals. For samples with x less than or equal to 0.0244, the short-range spin-Peierls correlations are found to start developing at simi lar to 15 K, independently of the Mg concentration. However, it turned out that the long-range order cannot be established unless the mean free path o f the spin excitations becomes longer than the length scale of the impurity distance. (C) 2000 Elsevier Science B.V. All rights reserved.