Tuning of the ferromagnetic and superconducting transitions by tin-doping in RuSr2GdCu2O8

Solid solutions Ru1-xSnxSr2GdCu2O8 with nominal compositions x= 0-0.4 have been prepared, although some secondary phases are also present. Powder x-ray diffraction:and:physical measurements show that Sn4+ substitutes only at the Ru sites in this layered material. Sn-doping :suppresses the ferromagnetic moment in the ruthenate layers, and the Curie temperature decreases from 138 K in the undoped material to 78 K for x = 0.4. This enhances the conductivity of the CuO2 planes and the onset of superconductivity increases from 36 K at x = 0 to 48 K at x= 0.2, but falls thereafter. This may reflect the increase in hole transfer to the CuO2 planes and the reduction of ferromagnetic order within the ruthenate layers. [S0163-1829(99)01746-3].