Magnetotransport study of the magnetic superconductors GdSr <inf>2</inf>Ru<inf>1 - X</inf>Cu<inf>2 + x</inf>O<inf>8</inf>

Magnetotransport studies were carried out for the ruthenocuprates GdSr 2Ru1 - xCu2 + xO8 (x = 0 and 0.05) in the temperature range 2-300K and in fields up to 9T. The electrical resistivity measurements near the superconducting region indicate that these compounds exhibit granular superconductivity. The magnetic field has significant effects on the intragranular superconducting transition temperature (T 1) as well as the inter-granular superconducting transition temperature (T2) which can be attributed to the microstructure as well as the large internal fields present in these compounds. The analysis of the magnetic field induced broadening of the resistivity transitions in these compounds suggests a two-dimensional nature for the vortex lattice. The magnetoresistance in the normal state is in general negative and its magnitude reaches a maximum around the magnetic transition temperature (TM). A positive magnetoresistance is observed at low fields for temperatures below TM in the parent compound which is absent in the Cu doped compound. The difference in the magnetoresistance behavior below TM is argued to be due to the weakening of the antiferromagnetic order upon Cu doping. © 2011 IOP Publishing Ltd.