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 sam ples RuSr2GdCu2O8 and RuSr2Gd1.4Ce0.6Cu2Oy are presented. Resistive measure ments in high magnetic fields show that the field dependence of the transit ion temperature is significantly different from those observed in other hig h-T-c cuprates. The sample RuSr2GdCu2O8 shows asystematic change in magneto resistance (MR): The MR is negative at temperatures above the magnetic orde ring temperature (T-Curie): Below T-Curie the MR displays a positive peak a t low fields, but becomes negative at high fields. However, the sample RuSr 2Gd1.4Ce0.6Cu2Oy shows a negative hlR in the whole measuring temperature ra nge. Both of the samples show a maximum negative magnetoresistance at about T-Curie. The specific heat anomaly is suppressed by the field, and the pea k-temperature slightly moves down with the field.