EPR STUDIES OF MN-DOPED YBA2CU3O7-DELTA COMPOSITES

The preliminary results of EPR experiments on superconducting Mn-YBaCu O composites are reported. The measurements were done in X band in the temperature range 4-300 K. Three distinct EPR components were observe d possessing different g-factors and a rather different temperature be havior. For similar nonsuperconducting samples, only two signals were observed. The nature of the different components is discussed from the comparison of the results. It is shown that, among the superconductin g samples, two of them originate from Mn2+ paramagnetic centers while the third one presumably comes From Cu2+ paramagnetic center. For the nonsuperconducting samples, a magnetic phase transition in an ordered state has been revealed at 25 K. This transition seems to be stimulate d by the presence of Mn ions or clusters, probably located in the CuO chains.