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 $J_1\mathrm{\text{−}}{J}_2$-spin model with ferromagnetic 1st and AFM 2nd neighbor in-chain exchange. A complex 3D-phase diagram has been found. For ${\mathrm{Li}}_2{\mathrm{CuO}}_2$ and ${\mathrm{Ca}}_2{\mathrm{Y}}_2{\mathrm{Cu}}_5{\mathrm{O}}_{10}$, we show that $H_s$ is solely determined by the IC and predict $H_s\approx 61\mathrm{T}$ for the latter. With $H_s\approx 55\mathrm{T}$ from magnetization data one reads out a weak IC for ${\mathrm{Li}}_2{\mathrm{CuO}}_2$ close to that obtained from inelastic neutron scattering.

• Received 19 April 2010

DOI:https://doi.org/10.1103/PhysRevLett.107.097201