Changes of the local distortions and colossal magnetoresistive properties of La(0.7)Ca(0.3)MnO(3) induced by Ti or Ga defects
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Changes of the local distortions and colossal magnetoresistive properties of La(0.7)Ca(0.3)MnO(3) induced by Ti or Ga defects

  • Author(s): Bridges, F.
  • Cao, D.
  • Anderson, M.
  • Ramirez, A.P.
  • Olapinski, M.
  • Subramanian, M.A.
  • Booth, C.H.
  • Kwei, G.
  • et al.
Abstract

The magnetoresistive properties of La0.7Ca0.3MnO3 change rapidly when Ti or Ga are substituted on the Mn site for concentrations, x, from 1 to 10 percent. The samples exhibit colossal magnetoresistance (CMR) and the resistivity increases dramatically with dopant concentration. The temperature of the resistivity peak, TR, shifts rapidly to lower temperatures with increasing x and the ferromagnetic transition broadens. However, the transition temperature, Tc, is only slightly suppressed. Consequently, TR occurs well below Tc for x above 2 percent. Investigations of these materials using Mn XAFS show that changes in the local structure, parametrized by the pair-distribution width, sigma, correlate well with Tc and the sample magnetization. For a given dopant, the resistivity peak occurs when sigma^2 decreases below a critical value. Both dopants produce extended defects which increases the resistivity of the nearby materials considerably. The data suggest that even at x~;4 percent, most of the sites are slightly distorted at low T.

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