Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

108 Biennial Report 2005-074.1.1.10 Charge ordering in nanoparticles of Pr 0.65 Ca 0.35 MnO 3The observation of charge order transition in bulk form of rare-earth based manganites is welldocumented. However, there is hardly any manifestation of this phenomenon when the grain sizeis reduced to nano meter scale. We have observed charge ordering in nanocrystallinePr 0.65 Ca 0.35 MnO 3 of average particle size 40 nm. The transport, magnetotransport, magnetizationand specific heat measurements have been performed on the nanocrystalline sample. Thespecific heat and magnetization studies have confirmed that the CO transition occurs in the sampleat 225 K.Fig.4.1.1.10. Large modification of low temperature resistance in presence of magneticfield - Magnetic field induced melting of Charge Ordered state.The charge order transition temperature is almost same as in case of the bulk form of the sample.Due to the CO, the resistivity increases abruptly with the decrease of temperature. In presenceof magnetic field, the CO state is switched over to the metallic state, giving rise to large negativemagnetoresistance. This is the first report regarding charge ordering in nanoparticles ofmanganites.Anis Biswas, Indranil DasECMP4.1.1.11 Magnetotransport studies in Pr 0.65 (Ca 1−x Sr x ) 0.35 MnO 3 nanoparticlesThe substitution of Sr in Ca- site of Pr 0.65 Ca 0.35 MnO 3 changes the Charge order behavior of thesample. The CO state is destabilized below a certain temperature resulting in a state compris-