High energy magnetic excitations from the edge-sharing CuO₂ chains in Ca₂Y₂Cu₅O₁₀

Ca₂Y₂Cu₅O₁₀ is a quasi-one-dimensional magnet, which consists of the ferromagnetic edge-sharing CuO₂ chains. It was previously reported from neutron inelastic scattering experiments in Ca₂Y₂Cu₅O ₁₀ up to ∼14 meV that in the magnetically ordered state there is an anomalous broadening of spin-wave excitations along the chain, which is caused mainly by the antiferromagnetic interchain interactions [M. Matsuda et al.: Phys. Rev. B 63 (2001) 180403(R)]. In this study we extended an energy range of the measurement up to ∼25 meV. The experimental result suggests that there exist two excitation modes, which is consistent with a theoretical result qualitatively. One mode corresponds to the relatively sharp spin-wave excitations, which broaden with increasing q_chain and disappear around q_chain ∼ 0.2 r.l.u. and ω ∼ 10 meV. Another one corresponds to the very broad excitations apparent at q_chain ∼ 0.2-0.3 r.l.u. and ω ∼ 12-25 meV.