Effects of in-chain and off-chain substitutions on spin fluctuationsin the spin-Peierls compoundCuGeO3

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. Inchain and off-chain substitutions quench the spin-Peierls state and induce 3D antiferromagnetic order at T≤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≤60 K 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. 75.50.Ee, 75.30.Et

Raman scattering from magnetic excitations in the spin-ladder compoundsCaV2O5andKonstantinović1, Popović2, Isobe3 et al. 2000Phys. Rev. B

“…(2) The intensity of the 795 cm −1 line saturates at temperatures below 80 K. In the case of the bound state the linear dependence of its intensity as a function of the temperature is believed to be the fingerprint of it, without saturation up to very low temperatures 17 . Thus, we assign the onset of the magnon continuum to 2∆ s =795 cm −1 and obtain the spin-gap in CaV 2 O 5 to be ∆ s =398 cm −1 (570 K).…”

Magnetoelastic coupling and spin excitations in the spin-gap system(VO)2P2<

“…15 K is larger than T SP . Therefore, in CuGeO 3 similar crossover phenomena are only observable in substituted samples 37 .…”

Dopant-bound spinons in Cu 1 − x Zn x GeO 3

“…Inelastic light scattering (ILS) is a sensitive technique to study magnetic excitations in pure [9,10,11,12,13,14] and doped CuGeO 3 [15,16,17]. It is the aim of the present Letter to show the existence of a so far unobserved type of magnetic scattering process in doped gapful low-dimensional spin systems which arises due to the presence of dopant-bound spinons (DBS).…”