Low Field Magnetotransport in Manganites

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The perovskite manganites of general formula RE₁-xAeₓMnO₃ (RE= rare earth,AE=Ca, Sr, Ba and Pb)have drawn considerable attention, especially following the discovery of colossal magnetoresistance (CMR). They exhibit extraordinary large magnetoresistance pronounced as CMR in the vicinity of insulator-metal/paramagnetic-ferromagnetic transition at a relatively large applied magnetic fields. However, for applied aspectes, occurence of significant CMR at low applied magnetic fields would be required. This review consists of of two sections: In the first section we have extensively reviewed the salient features e.g. structure, phase diagram, double exchange mechansim, Jahn Teller effect, different types of ordering and phase separation of CMR mangnaites. The second is devoted to an overview of experimental results on CMR and related magnetotransport characteristics at low magnetic fields for doped manganites such as polycrystalline La₀.67Ca₀.33MnO₃ films, Ag admixed La₀.67Ca₀.33MnO₃ films, polycrystalline (La₀.7Ca₀.2Ba₀.1MnO₃)and epitaxial (La₀.67Ca₀.33MnO₃) films on different substrates, nanophasic La₀.7Ca₀.3MnO₃, mangnaite-polymer composites (La₀.7Ba₀.2Sr₀.1MnO₃-PMMA and La₀.67Ca₀.33MnO₃-PMMA)and double layered polycrystalline (La₁.4Ca₁.6-xBaₓMn₂O₇) and films (La₁.4Ca₁.6Mn₂O₇). Some other potential magnetoresistive materials e.g. pyrochlores, chalcogenides, ruthenates, diluted magnetic semiconductors, magnetic tunnel junctions, nanocontacts etc have aslo been briefly dealt with. The review concludes with the summary of results for low field magnetotransport behaviour and prospectes for applications.