Effect of Ca substitution on crystal structure and superconducting properties of ferromagnetic superconductor RuSr2−xCaxGd1.4Ce0.6Cu2O10−δ

► We examined the effect of Ca substitution for Sr on electrical and magnetic properties of Ru1222. ► Replacement of Sr with Ca reduces the interlayer distance of CuO2 and RuO2 layers. ► The onset superconducting transition temperature is dropped by Ca substitution. ► We observed the variation of the hopping exponent p across magnetic transition at Tm.