The surface impedance, Z(s) = R-s + iX(s), of several GdBa2Cu3O7-delta single crystals has been measured in the temperature range of 1.2-40 K. The complex conductivity, sigma = sigma(1) - i sigma(2), is extracted and the real part of the conductivity is found to be enhanced below 15 K reaching a peak at temperatures of the order of 3 K. sigma(1) then drops rapidly and is consistent with an antiferromagnetic phase transition at 2.2 K. Using a modified model for surface impedance the spin relaxation time is found to increase rapidly below the Neel temperature. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 4]
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