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Changes of the local distortions and colossal magnetoresistive properties of La0.7Ca0.3MnO3 induced by Ti or Ga defects

01 January 2001

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The magnetoresistive properties of La0.7Ca0.3MnO3 change rapidly when Ti or Ga is substituted on the Mn site for concentrations, x, from 1 to 10%. The samples exhibit colossal magnetoresistance (CMR) and the resistivity increases dramatically with dopant concentration. The temperature of the resistivity peak, T-R, shifts rapidly to lower temperatures with increasing x, and the ferromagnetic transition broadens. However, the transition temperature, T-c is only slightly suppressed. Consequently T-R occurs well below T-c for x above 2%. Investigations of these materials using Mn XAFS show that changes in the local structure, parameterized by the pair-distribution width, sigma, correlate with T-c 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 material considerably. The data suggest that even at similar to4% most of the sites are slightly distorted at low T.