Coexistence of superconductivity and ferromagnetism in 1212-Ru1-xMxSr2GdCu2O8 (M=Ti, V, Nb)

The coexistence of superconductivity and ferromagnetism in 1212-RuSr2GdCu2O8 is unique among high-T-c materials. Samples of Ru1-xMxSr2GdCu2O8, with M=Ti, V and Nb; and 0 less than or equal tox less than or equal to1, were prepared to elucidate the role of the RuO2 planes in this interesting layered 1212 cuprate. The solubility ranges of M =Ti and V are limited to x<0.15 whereas that of Nb extends to full substitution. In all cases superconductivity is lost at higher substitution levels (x>0.2), however with vanadium substitution the T-c increases from 20 K to 25 K. The ferromagnetism of the RuO2 layers is dramatically affected by the electronic configuration of the substituting ion, weakened for M=Ti and Nb and enhanced for M=V. These results indicate that the superconductivity and ferromagnetism are intimately linked to the layered architecture of this 1212 structure. (C) 2000 Elsevier Science Ltd. All rights reserved.