Heat capacity and transport studies of the ferromagnetic superconductor RuSr2GdCu2O8

Resistivity, thermoelectric power, and heat capacity are investigated in th e ferromagnetic superconductor RuSr2GdCu2O8 with and without Zn substitutio n. The thermodynamic signatures of the ordering of the Ru moments and the p aramagnetic Gd moments as well as the onset of superconductivity are all cl early seen and quantified. The materials are shown to exhibit bulk supercon ductivity which coexists with spatially uniform ferromagnetism. They appear to be typical underdoped superconducting cuprates in which the pseudogap d ominates normal-state transport, thermodynamic, and substitutional properti es. However, a field-induced increase in T-c could suggest some degree of t ripler pairing.