Transport properties and specific heat of RuSr2GdCu2O8 and RuSr2Gd1.4Ce0.6Cu2Oy in magnetic fields -: art. no. 064506

The magnetoresistance (MR) and specific heat in magnetic fields for the samples RuSr2GdCu2O8 and RuSr2Gd1.4Ce0.6Cu2Oy are presented. Resistive measurements in high magnetic fields show that the field dependence of the transition temperature is significantly different from those observed in other high-T-c cuprates. The sample RuSr2GdCu2O8 shows asystematic change in magnetoresistance (MR): The MR is negative at temperatures above the magnetic ordering temperature (T-Curie): Below T-Curie the MR displays a positive peak at low fields, but becomes negative at high fields. However, the sample RuSr2Gd1.4Ce0.6Cu2Oy shows a negative hlR in the whole measuring temperature range. Both of the samples show a maximum negative magnetoresistance at about T-Curie. The specific heat anomaly is suppressed by the field, and the peak-temperature slightly moves down with the field.