Thermodynamic parameters of theT=0, spin-1/2 square-lattice Heisenberg antiferromagnet

Transverse susceptibility (${\chi }_{\perp }$), spin stiffness constant (${\rho }_s$), spin-wave velocity ($c_s$), staggered magnetization ($M^{+}$) and the ground-state energy ($E_0$) of the T=0, spin-(1/2 square-lattice Heisenberg antiferromagnet are estimated by expansions around the Ising limit. Extrapolations of the series, which take into account the leading singular behavior, give $Z_{\chi }$(=8${\chi }_{\perp }$J)=0.52±0.03, &(=4${\mathrm{\rho }}_{\mathrm{s}}$/J)=0.72 &(=${\mathrm{c}}_{\mathrm{s}}$/ √2 J)=1.18±0.02, 2$M^{+}$=0.605±0.015, and 4$E_0$/J=-2.6785±0.0010. The extrapolations are aided by universal amplitude ratios, whose values can be obtained exactly from the spin-wave theory.