Coexistence of dimerization and long-range magnetic order in the frustrated spin-chain system LiCu₂O₂: Inelastic light scattering study

Raman scattering studies of the frustrated spin chain system LiCu₂O₂ are reported. Two transitions into a magnetically ordered phase (taken place at temperatures ∼9 and ∼24K) have been confirmed from the analysis of optical properties of the samples. Interestingly, two different magnetic excitations, seen at 100 and 110cm^-1 in the magnetically ordered phase superimpose each other independently, indicating a coherent coexistence of long-range magnetic order and dimerization. The observed phenomenon is attributed to magnetostructural peculiarities of LiCu₂O₂ leading to the intrinsic presence of magnetic/nonmagnetic impurities on a nanometer scale. In particular, magnetic impurities play a significant role in driving the transition from an incommensurate state to a Néel ordered one at 9 K.