  We report inelastic neutron scattering experiments in Ca2Y2Cu5O10 and map out
the full one magnon dispersion which extends up to a record value of 53 meV for
frustrated ferromagnetic (FM) edge-sharing CuO2 chain (FFESC) cuprates. A
homogeneous spin-1/2 chain model with a FM nearest-neighbor (NN), an
antiferromagnetic (AFM) next-nearest-neighbor (NNN) inchain, and two diagonal
AFM interchain couplings (ICs) analyzed within linear spin-wave theory (LSWT)
reproduces well the observed strong dispersion along the chains and a weak one
perpendicularly. The ratio R=|J_{a2}/J_{a1}| of the FM NN and the AFM NNN
couplings is found as ~0.23, close to the critical point Rc=1/4 which separates
ferromagnetically and antiferromagnetically correlated spiral magnetic ground
states in single chains, whereas Rc>0.25 for coupled chains is considerably
upshifted even for relatively weak IC. Although the measured dispersion can be
described by homogeneous LSWT, the scattering intensity appears to be
considerably reduced at ~11.5 and ~28 meV. The gap-like feature at 11.5 meV is
attributed to magnon-phonon coupling whereas based on DMRG simulations of the
dynamical structure factor the gap at 28 meV is considered to stem partly from
quantum effects due to the AFM IC. Another contribution is ascribed to the
intrinsic superstructure from the distorting incommensurate pattern of CaY
cationic chains adjacent to the CuO2 ones. It gives rise to non-equivalent CuO4
units and Cu-O-Cu bond angles Phi and a resulting distribution of all exchange
integrals. The J's fitted by homogeneous LSWT are regarded as average values.
The record value of the FM NN integral J1=24 meV among FFESC cuprates can be
explained by a non-universal Phi (not 90 deg.) and Cu-O bond length dependent
anisotropic mean direct FM Cu-O exchange K_{pd}~120 meV. Enhanced K_{pd} values
are also needed to compensate a significant AFM J_{dd} > ~6 meV.
