Ca(2)Y(2)Cu(5)O(10): the first frustrated quasi-1D ferromagnet close to criticality.

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.

Saturation field of frustrated chain cuprates: broad regions of predominant interchain coupling.

A thermodynamic method to extract the interchain coupling (IC) of spatially anisotropic 2D or 3D spin-1/2 systems from their empirical saturation field H(s) (T=0) is proposed. Using modern theoretical methods we study how H(s) is affected by an antiferromagnetic (AFM) IC between frustrated chains described in the J(1)-J(2)-spin model with ferromagnetic 1st and AFM 2nd neighbor in-chain exchange. A complex 3D-phase diagram has been found.

7Li NMR investigation of Li-Li pair ordering in the paraelectric phase of weakly substitutionally disordered K(1-x)Li(x)TaO3.

Breaking of the average cubic symmetry in Li-doped potassium tantalate was observed with quadrupole-perturbed 7Li NMR at temperatures (150-400 K) far above the nominal glass transition temperature (≈50  K for Li concentration x=0.03). The observed spectrum consists of contributions from both isolated Li ions (i.