Anomalous Magnetotransport Properties of Bi Doped La0.67Sr0.33MnO3

We have studied the magnetotransport properties of La0.67−xBixSr0.33MnO3 (x = 0, 0.3, 0.4, 0.5). The x ≤ 0.3 samples show metal–insulator transitions, whereas x ≥ 0.4 samples exhibit an insulating behaviour at zero field. Notably, two low-temperature upturns were observed for La0.37Bi0.3Sr0.33MnO3, which indicates the existence of two different mechanisms. La0.27Bi0.4Sr0.33MnO3 shows field-induced metallic behavior due to the melting of charge ordering with applied magnetic field. A large magnetoresistance of ∼100% is observed for La0.27Bi0.4Sr0.33MnO3 at ∼90 K. On the other hand, La0.37Bi0.3Sr0.33MnO3 exhibits a nearly constant large magnetoresistance of ∼80% between ∼30 and 250 K, which decreases outside this temperature range. The observed anomalous low-temperature magnetotransport properties of La0.67−xBixSr0.33MnO3 are shown to arise from the coexisting phases of ferromagnetic metallic and antiferromagnetic charge-ordered insulating states.