Fluctuating magnetic order in YBa2Cu3O7 substituted with both Fe and Co: aFe-57 Mossbauer spectroscopy study

We report a Fe-57 Mossbauer study of superconducting samples of YBa2Cu3O7 s ubstituted with 1% Fe and also, in addition, up to 4% Co. Increasing the Co level has no influence on the 57Fe quadrupole interactions but strongly in creases the saturated Fe-57 hyperfine fields. For the sample with 4% Co, wh ere the increased hyperfine field leads to a reduced interference between t he magnetic subspectra, we carry out a quantitative analysis of the thermal dependence of the fluctuation rate of the Fe-57 hyperfine held. We compare the properties of the short-range correlated magnetic order introduced by the Co/Fe as sensed by the perturbing Fe-57 probe with those reported previ ously for the non-perturbing Mossbauer probe Yb-170 in the same system. (C) 1999 Elsevier Science B.V. All rights reserved.