The effects of quenched dipole moments on a two-dimensional Heisenberg anti
ferromagnet are found exactly, by applying the renormalization group to the
appropriate classical non-linear sigma model. Such dipole moments represen
t random fields with power law correlations. At low temperatures, they also
represent the long range effects of quenched random strong ferromagnetic b
onds on the antiferromagnetic correlation length, xi(2D), of a two-dimensio
nal Heisenberg antiferromagnet. It is found that the antiferromagnetic long
range order is destroyed for any non-zero concentration, x, of the dipolar
defects, even at zero temperature. Below a line T proportional to x, where
T is the temperature, xi(2D) is independent of T, and decreases exponentia
lly with x. At higher temperatures, it decays exponentially with rho(s)(eff
)/T, with an effective stiffness constant rho(s)(eff), which decreases with
increasing x/T. The latter behavior is the same as for annealed dipole mom
ents, and we use our quenched results to interpolate between the two types
of averaging for the problem of ferromagnetic bonds in an antiferromagnet.
The results are used to estimate the three-dimensional Neel temperature of
a lamellar system with weakly coupled planes, which decays linearly with a:
at small concentrations, and drops precipitously at a critical concentrati
on. These predictions are shown to reproduce successfully several of the pr
ominent features of experiments on slightly doped copper oxides.