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Science 25 July 1997:
Vol. 277. no. 5325, pp. 546 - 549
DOI: 10.1126/science.277.5325.546
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Reports

Large Enhancement of Magnetoresistance in Tl2Mn2O7: Pyrochlore Versus Perovskite

A. P. Ramirez, M. A. Subramanian

The synthesis of and magneto-transport in the "colossal magnetoresistance" (CMR) pyrochlore-structure compounds Tl2-xScxMn2O7 for 0 <= x <= 0.5 are reported. The maximum resistivity (rho ) increases by 105 while the Curie temperature (Tc) 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 rho  and Tc 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.

A. P. Ramirez, Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, NJ 07974-0636, USA.
M. A. Subramanian, DuPont Central Research and Development, Experimental Station, Wilmington, DE 19880-0328, USA.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)