Electrical and magnetic properties of Ru1-xMxSr2GdCu2O8 (M = Ti, V and Nb)

Samples of Ru1-xMxSr2GdCu2O8, with M = Ti, V and Nb; and 0 less than or equ al to x less than or equal to 1, were synthesized to shed light on the role of the RuO2 planes in this 1212-type compound which is a ferromagnetic sup erconductor (T-c = 10-40 K) when x = 0. We show that the ferromagnetism and the superconductivity are weakened for M = Ti and Nb, and enhanced for M = V although superconductivity is suppressed for all samples of higher dopin g levels (x > 0.2). Jonker analysis of the high-temperature electrical prop erties of RuSr2GdCu2O8 shows that it falls within the characteristic range for other known superconductors.