Low Field Magnetotransport in Manganites
  The perovskite manganites of general formula RE_1-xAe_xMnO_3 (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 La_0.67Ca_0.33MnO_3 films, Ag admixed La_0.67Ca_0.33MnO_3 films, polycrystalline (La_0.7Ca_0.2Ba_0.1MnO_3)and epitaxial (La_0.67Ca_0.33MnO_3) films on different substrates, nanophasic La_0.7Ca_0.3MnO_3, mangnaite-polymer composites (La_0.7Ba_0.2Sr_0.1MnO_3-PMMA and La_0.67Ca_0.33MnO_3-PMMA)and double layered polycrystalline (La_1.4Ca_1.6-xBa_xMn_2O_7) and films (La_1.4Ca_1.6Mn_2O_7). 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. 
P.K.Siwach, H.K.Singh and O.N.Srivastava