https://doi.org/10.1007/s100510050719
Suppression of antiferromagnetic correlations by quenched dipole-type impurities
School of Physics and Astronomy,
Raymond and Beverly Sackler Faculty
of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
Received:
22
October
1998
Published online: 15 April 1999
The effects of quenched dipole moments on a two-dimensional
Heisenberg
antiferromagnet are found exactly, by applying the renormalization group
to the appropriate classical non-linear
sigma model.
Such dipole moments represent random fields with power law correlations.
At low temperatures, they also represent the long range effects of
quenched random strong ferromagnetic bonds
on the antiferromagnetic
correlation length, 
,
of a two-dimensional 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 
, where T is the temperature, is
independent
of T, and decreases exponentially with x. At higher temperatures, it
decays exponentially with 
, with an effective
stiffness constant 
, which decreases with
increasing x/T.
The latter behavior is the same as for annealed dipole moments, 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 Néel temperature of a
lamellar system with weakly coupled planes, which
decays linearly with x at small concentrations, and drops precipitously at
a critical concentration. These predictions are
shown to reproduce successfully
several of the prominent features of experiments on
slightly doped copper oxides.
PACS: 75.10.-b – General theory and models of magnetic ordering / 75.10.Nr – Spin-glass and other random models / 75.50.Ee – Antiferromagnetics
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999
