MOSSBAUER-SPECTROSCOPY OF FE-57 IN HIGH-TC SUPERCONDUCTORS YBA2FE3XCU3(1-X)O7-DELTA

Moessbauer spectroscopy of **5**7Fe in both tetragonal and orthorhombic phases of YBa//2(Fe//xCu//1// minus //x)//3O//7// minus // delta , with x equals 0. 01, 0. 02 and 0. 10, at temperatures 4. 2 K, 75 K, 90 K, and 300 K have been performed. In all samples three major subspectra corresponding to iron in different local environments are observed. It is concluded that Fe substitutes mainly Cu1. At 4. 2 K, samples with x equals 0. 01 in the 'quenched' tetragonal phase exhibit magnetic hyperfine structure, due to slow spin relaxation rates, whereas in the orthorhombic superconducting phase, only samples with x equals 0. 1 exhibit magnetic hyperfine structure, in this case probably due to spin glass magnetic order.