Large Enhancement of Magnetoresistance in Tl 2 Mn 2 O 7 : Pyrochlore Versus Perovskite

Abstract

The synthesis of and magneto-transport in the “colossal magnetoresistance” (CMR) pyrochlore-structure compounds Tl _{2 − x} Sc _x Mn ₂ O ₇ for 0 ≤ x ≤ 0.5 are reported. The maximum resistivity (ρ) increases by 10 ⁵ 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 (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.