We report a synchrotron x-ray scattering study of the diluted spin-Peierls (SP) material Cu_{1-x}Mg_xGeO_3. In a recent paper we have shown that the SP dimerization attains long-range order only for x < x_c = 0.022(0.001). Here we report that the SP transition is reentrant in the vicinity of the critical concentration x_c. This is manifested by broadening of the SP dimerization superlattice peaks below the reentrance temperature, T_r, which may mean either the complete loss of the long-range SP order or the development of a short-range ordered component within the long-range ordered SP state. Marked hysteresis and very large relaxation times are found in the samples with Mg concentrations in the vicinity of x_c. The reentrant transition is likely related to the competing Neel transition which occurs at a temperature similar to T_r. We argue that impurity-induced competing interchain interactions play an essential role in these phenomena.
@article{arxiv.cond-mat/9908369,
title = {Reentrant Spin-Peierls Transition in Mg-Doped CuGeO_3},
author = {V. Kiryukhin and Y. J. Wang and S. C. LaMarra and R. J. Birgeneau and T. Masuda and I. Tsukada and K. Uchinokura},
journal= {arXiv preprint arXiv:cond-mat/9908369},
year = {2009}
}