Large Enhancement of Magnetoresistance in Tl2Mn2O7: Pyrochlore Versus Perovskite

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Science  25 Jul 1997:
Vol. 277, Issue 5325, pp. 546-549
DOI: 10.1126/science.277.5325.546

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The synthesis of and magneto-transport in the “colossal magnetoresistance” (CMR) pyrochlore-structure compounds Tl2 xScxMn2O7for 0 ≤ x ≤ 0.5 are reported. The maximum resistivity (ρ) increases by 105 while the Curie temperature (T c) decreases by only 25% between x = 0 and 0.4. For x = 0.2 to 0.3, the magnetoresistance at both high field (6 tesla) and low field (<0.05 tesla) are significantly enhanced over the undoped (x = 0) compound. Structural analysis indicates that all of the manganese ions are near the +4 oxidation state. The behavior of ρ and T c suggests that scandium substitution affects mainly electronic conduction on the thallium-oxygen sublattice while leaving the magnetism essentially unchanged. These results demonstrate a distinct way of manipulating magneto-transport properties in CMR materials.

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