Enhancement of low-field magnetoresistance in Ce doped manganite Sm0.55Sr0.45MnO3

We report on the magnetization, resistivity and magnetoresistance measurements on polycrystalline samples of Sm0.55Sr0.45−xCexMnO3 (x=0 and 0.05). Substitution of Ce(x=0.05) reduced the para–ferromagnetic transition from ∼140 K (x=0) to ∼90 K. For x=0, the colossal magnetoresistance (CMR) (−100(ρB−ρ0)/ρ0) effect of 55% (143 K) was observed in a field of 0.6 Oe. On the other hand, for the x=0.05 sample, at 93 K, the CMR effect which was 32% in the field of 65 Oe increased to 87% in the field of 0.6 T. Our data rule out grain boundary effects as the principal cause but point out the applicability of the phase separation model.