Colossal magnetoresistance properties of Nd-doped Bi<inf>0.5</inf>Sr <inf>0.5</inf>MnO<inf>3</inf>

We have studied structure, transport, and magnetic properties of Ndx Bi0.5-x Sr0.5 Mn O3 (NBSMO) (x=0.2 and 0.4) through x-ray diffraction, magnetoresistance, and magnetization measurements. The Rietveld analysis of the x-ray diffraction data shows that the NBSMO crystallizes in an orthorhombic perovskite structure with Pbnm space group for x=0.2 and Imma space group for x=0.4. The lattice variations indicate that the highly polarizable 6 s2 lone pair of Bi ion is screened and the structural changes occur in accordance with change in the average radius of A -site cations. Magnetotransport studies reveal that both samples are variable range hopping semiconductors and the hopping depends on the orientation of localized spin moment of the electrons. Magnetic studies confirm that substituting Bi with Nd collapses the charge ordered antiferromagnetic (AFM) state of Bi0.5 Sr0.5 Mn O3 to ferromagnetic state, with TC 's∼276 and ∼278 K, for x=0.2 and 0.4, respectively. The observed enhancement in colossal magnetoresistance effect in NBSMO compared to Bi0.5 Sr0.5 Mn O3 is attributed to the presence of competing ferromagnetic and charge ordered AFM state. © 2008 American Institute of Physics.