Structural and magnetotransport properties of the CMR Tl_2Mn_2O7 pyrochlore
Abstract
Tl_2Mn_2O7 shows CMR (colossal magnetoresistance) effect but differs both structurally and electronically from perovskite manganese oxides. The crystal structure and its variation with temperature of this material are investigated. Structure refinement from the neutron powder diffraction data reveals that Tl_2Mn_2O7 has nearly stoichiometric composition and is crystallized in the cubic-pyrochlore type structure with a characteristic Mn-O-Mn bond angle of 133^circ. There is no structural anomaly associated with the change in magnetotransport properties at 142 K, suggesting weak spin-lattice and charge-lattice correlations. Despite the similarity of magnetotransport properties observed in the perovskite and the pyrochlore CMR materials, the double-exchange mechanism, which is usually applied to the perovskite oxides, does not seem to explain the behavior in the pyrochlore Tl_2Mn_2O7 compound. A superexchange-type interaction may stabilize the ferromagnetic ordering of Mn spins and cause the metallic conduction at low temperatures in Tl_2Mn_2O_7.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1997
- Bibcode:
- 1997APS..MAR.F2310S