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Effects of in-chain and off-chain substitutions on spin fluctuations in the spin-Peierls compound CuGeO_3

P. Lemmens·M. Fischer·G. Güntherodt·C. Gros·P. G. J. van Dongen·M. Weiden·W. Richter·C. Geibel·F. Steglich
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Abstract

The effect of in-chain and off-chain substitutions on 1D spin fluctuations in the spin-Peierls compound CuGeO_3 has been studied using Raman scattering in order to understand the interplay between defect induced states, enhanced spin-spin correlations and the ground state of low dimensional systems. In-chain and off-chain substitutions quench the spin-Peierls state and induce 3D antiferromagnetic order at T\leq 5 K. Consequently a suppression of a 1D gap-induced mode as well as a constant intensity of a spinon continuum are observed at low temperatures. A 3D two-magnon density of states now gradually extends to higher temperatures T\leq 60K compared with pure CuGeO_3. This effect is more pronounced in the case of off-chain substitutions (Si) for which a Néel state occurs over a larger substitution range, starting at very low concentrations. Besides, additional low energy excitations are induced. These effects, i.e. the shift of a dimensional crossover to higher temperatures are due to an enhancement of the spin-spin correlations induced by a small amount of substitutions. The results are compared with recent Monte Carlo studies on substituted spin ladders, pointing to a similar instability of coupled, dimerized spin chains and spin ladders upon substitution.

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P. Lemmens, M. Fischer, G. Güntherodt, C. Gros, P. G. J. van Dongen, M. Weiden, W. Richter, C. Geibel, F. Steglich. 1997-03-06. Effects of in-chain and off-chain substitutions on spin fluctuations in the spin-Peierls compound CuGeO_3. https://doi.org/10.1103/physrevb.55.15076

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