Variation of electrical and magnetic properties in La_0.67-xGd_xCa_0.33MnO₃ perovskites

We have investigated the variation of electrical and magnetic properties in polycrystalline La_0.67-xGd_xCa_0.33MnO₃ with the change of gadolinium content. As x increases, we observed a transition from the ferromagnetic state to the canted ferromagnetic state at x = 0.10. The magnetization and conductivity show considerable thermal hysteresis in the samples with x = 0.10 and 0.15, and magnetoresistance is larger than 65 and 90% over a temperature range approx. 30 K, respectively. Based on the sample with x = 0.15 we found an abnormal increase in magnetization in low temperatures which should be attributed to the contribution of paramagnetic gadolinium ions. For x = 0.20 and 0.25 samples, insulator conduction has been observed above 80 K, and magnetoresistance approx. 55% has been detected in the sample with x = 0.20.