MAGNETISM AND SUPERCONDUCTIVITY IN R1.5CE0.5MSR2CU2O10-DELTA (M = RU AND FE) COMPOUNDS

It is shown here, that the superconducting (SC) R1.5Ce0.5RuSr2Cu2O10-d elta (RCeRuSCO, R = Eu and Gd) materials (T-c similar to 32 and 42 K) are also antiferromagnetically (AFM) ordered at T-N(Ru) similar to 122 and 180 K, respectively, thus, T-N much greater than T-c, a trend whi ch is contrary to that obtained in ''magnetic-SC'' intermetallic syste ms. Mossbauer spectroscopy (MS) on 0.5% Fe-57 doped samples shows that all Fe ions reside in the Ru site which is magnetically ordered, wher eas SC is confined to the CuO2 planes. On the other hand, for Y1.5Ce0. 5FeSr2Cu2O9 (YCeFSCO) no SC is found and the Cu-O planes order AFM at T-N(Cu) = 31 K. MS studies reveal two in equivalent Fe sites, and that Fe resides predominantly (60%) in the Cu(1) site. In both sites, the Fe does not order magnetically, and the low T-N(Cu) obtained is due to frustration of the Cu moments by the presence of Fe. T-N is sensitive to oxygen concentration and shifts toward 260 K when oxygen is deplet ed.