Physical characterization of RuSr2GdCu2O8 sintered samples: An analysis of the magnetic measurements performed by a SQUID magnetometer

In this paper we present the resistive and magnetic characterization of sintered RuSr2GdCu2O8 samples. We show how the physical properties, related both to the superconducting and magnetic state, are affected by the final annealing step: one week in flowing oxygen. In doing so we perform a detailed analysis of the complexity of the dc magnetic measurements performed on such type of samples below the superconducting transition: in particular we discuss the structural and experimental reasons that make magnetic measurements in such a system so difficult. These reasons come from the simultaneous presence of two magnetic lattices and of the diamagnetism related to the superconducting state. The situation justifies, at least in part, the wide spread of results presented in the literature and the controversial visibility of the Meissner effect. We remark moreover the not negligible effect of the residual field and how it is possible to take it, at least in the zero field cooled magnetic procedure, into account.