Suppression of antiferromagnetic correlations by quenched dipole-type impurities |
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Authors: | V Cherepanov IY Korenblit A Aharony O Entin-Wohlman |
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Institution: | (1) School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel, IL |
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Abstract: | 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.
Received 22 October 1998 |
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Keywords: | PACS 75 10 -b General theory and models of magnetic ordering - 75 10 Nr Spin-glass and other random models - 75 50 Ee Antiferromagnetics |
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