1201.6663 (R. O. Kuzian et al.)

Ca2Y2Cu5O10: the first frustrated quasi-1D ferromagnet close to
criticality    [PDF]

R. O. Kuzian, S. Nishimoto, S. -L. Drechsler, J. Malek, S. Johnston, J. van den Brink, M. Schmitt, H. Rosner

Ca2Y2Cu5O10 is build up from edge-shared CuO4 plaquettes forming spin chains.
From inelastic neutron scattering data we extract an in-chain nearest neighbor
exchange J1 approximately -170 K and the frustrating next neighbor J2
approximately 32 K interactions, both significantly larger than previous
estimates. The ratio alpha= J2/J1 approximately 0.19 places the system very
close to the critical point alpha_c=0.25 of the J1-J2 chain, but in the
ferromagnetic regime. We establish that the vicinity to criticality only
marginally affects the dispersion and coherence of the elementary
spin-wave-like magnetic excitations, but instead results in a dramatic
T-dependence of high-energy Zhang-Rice singlet excitation intensities.

View original: http://arxiv.org/abs/1201.6663