Tuning of the superconducting and ferromagnetic transitions by Cu doping for Ru in GdSr2RuCu2O8

In order to explore the possibility of tuning superconducting and ferromagnetic transitions by Cu doping (for Ru) in GdSr2RuCu2O8, we have carried out synthesis and characterization of GdSr2Ru1−xCu2+xO8 (x=0, 0.05, 0.1 and 0.2) and studied their physical properties. Coexistence of superconductivity and ferromagnetism is observed in all the Cu doped samples studied here. The zero field susceptibility data suggests formation of a spontaneous vortex phase. Cu doping decreases the ferromagnetic Curie temperature, whereas the superconducting transition temperature increases until an optimal concentration x∼0.1. This reflects an increase in hole transfer to the CuO2 planes and reduction of ferromagnetic order within the ruthenate layers.