  We study the destruction of the antiferromagnetic order in the high-Tc
superconductors La(2-x)Sr(x)CuO(4) and YBa(2)Cu(3)O(6+x) in the framework of
the CP1-nonlinear sigma model formulation of the 2D quantum Heisenberg
antiferromagnet. The dopants are introduced as independent fermions with
appropriate dispersion relations determined by the shape of the Fermi surface.
The energy of skyrmion topological defects, which are shown to be introduced by
doping, is used as an order parameter for antiferromagnetic order. We obtain
analytic expressions for this as a function of doping which allow us to plot
the curves T_N(x_c)\times x_c and M(x)\times x, for both YBCO and LSCO, in good
quantitative agreement with the experimental data.
