title: Ca(2)Y(2)Cu(5)O(10): the first frustrated quasi-1D ferromagnet close to criticality.
abstract: Ca(2)Y(2)Cu(5)O(10) is built up from edge-shared CuO(4) plaquettes forming spin chains. From inelastic neutron scattering data we extract an in-chain nearest-neighbor exchange J(1)≈-170  K and the frustrating next-neighbor J(2)≈32  K interactions, both significantly larger than previous estimates. The ratio α=|J(2)/J(1)|=0.19±0.01 places the system close to the critical point α(c)=0.25 of the J(1)-J(2) chain but in the 1D ferromagnetic regime. We establish that the vicinity to criticality only marginally affects the dispersion and coherence of the spin-wave-like magnetic excitations but instead results in a dramatic T dependence of high-energy Zhang-Rice singlet excitation intensities.
authors.affiliation: Institute for Theoretical Solid State Physics, IFW Dresden, 01171 Dresden, Germany.
authors.forename: R O
authors.initials: RO
authors.lastname: Kuzian
authors.forename: S
authors.initials: S
authors.lastname: Nishimoto
authors.forename: S-L
authors.initials: SL
authors.lastname: Drechsler
authors.forename: J
authors.initials: J
authors.lastname: Málek
authors.forename: S
authors.initials: S
authors.lastname: Johnston
authors.forename: Jeroen
authors.initials: J
authors.lastname: van den Brink
authors.forename: M
authors.initials: M
authors.lastname: Schmitt
authors.forename: H
authors.initials: H
authors.lastname: Rosner
authors.forename: M
authors.initials: M
authors.lastname: Matsuda
authors.forename: K
authors.initials: K
authors.lastname: Oka
authors.forename: H
authors.initials: H
authors.lastname: Yamaguchi
authors.forename: T
authors.initials: T
authors.lastname: Ito