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

The coexistence of superconductivity and ferromagnetism in 1212-RuSr2GdCu2O 8 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 pre pared 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 wh ereas that of Nb extends to full substitution. In all cases superconductivi ty is lost at higher substitution levels (x>0.2), however with vanadium sub stitution the T-c increases from 20 K to 25 K. The ferromagnetism of the Ru O2 layers is dramatically affected by the electronic configuration of the s ubstituting ion, weakened for M=Ti and Nb and enhanced for M=V. These resul ts indicate that the superconductivity and ferromagnetism are intimately li nked to the layered architecture of this 1212 structure. (C) 2000 Elsevier Science Ltd. All rights reserved.