Low frequency transport measurements in GdSr2RuCu2O8

Low frequency transport measurements are performed on GdSr$_2$RuCu$_2$O$_8$ pellets. The observed current-voltage curves are qualitatively explained in the framework of a simple phenomenological model accounting for coexistence of ferromagnetism and superconductivity in the sample. A Curie temperature $T_{cM}$=133 K and a superconducting critical temperature $T_{cS}$=18 K, with an onset temperature $T_{cO}$=33 K, are extracted from the analysis of the current-voltage curves.