Hall effect, thermopower and electrical resistivity of doped RuSr ₂GdCu₂O₈ system

Polycrystalline samples of Ru_1-xSb_xSr ₂GdCuO₈ doped with Sb, in which magnetic order and superconductivity coexist with T_magnetic ≫ TC, were prepared by a solid state reaction technique. Lattice parameters, electrical resistivity, Hall and thermopower coefficients measurements on the same sintered ceramic samples are presented. Both Hall effect and thermopower show anomalous decreases below T_magnetic which might be explained with a simple two-band model in the RuO₂ layer at T_magnetic. It was also observed that the Sb doping reduce the conductivity of the system and the transition temperature decreases with increasing Sb content. This may be due to a distortion of RuO₆ octahedra which is responsible for the increase of hole localization.