Colossal magnetoresistance without Mn3+/Mn4+ double exchange in the stoichiometric pyrochlore Tl2Mn2O7

Science

Volumn 273, Issue 5271, 1996, Pages 81-84

  Subramanian, M A ^a   Toby, B H ^b   Ramirez, A P ^c   Marshall, W J ^a   Sleight, A W ^d   Kwei, G H ^e  

^a DUPONT COMPANY   (United States)

^b NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY   (United States)

^c LUCENT TECHNOLOGIES   (United States)

^d OREGON STATE UNIVERSITY   (United States)

^e LAWRENCE LIVERMORE NATIONAL LABORATORY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

MANGANESE;

ARTICLE; ELECTRIC RESISTANCE; ELECTROMAGNETIC FIELD; MAGNETIC FIELD; PRIORITY JOURNAL; STOICHIOMETRY; X RAY DIFFRACTION;

EID: 0030036838     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.273.5271.81     Document Type: Article

References (34)

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18. The sample was weighed before and after the reaction to check for thallium evaporation; the results showed virtually no weight change. Microprobe analysis showed that the Mn:Tl ratio is 0.99 ± 0.01. No reflections due to impurities were observed in the powder XRD pattern. Microscopic examination of the pellet revealed the formation of several small single crystals, which were mechanically removed and used for the single-crystal XRD studies.
19. The dc magnetization M was measured as a function of temperature with a commercial superconducting quantum interference device (SQUID) magnetometer between 5 and 300 K and for magnetic fields up to 4 T. The resistivity (p) was measured by a standard in-line, four-probe technique and a commercial ac resistance bridge (operating at 16 Hz) at temperatures between 5 and 300 K and at magnetic fields up to 8 T.
20. Data were collected at 298 and 50 K with a Cu(220) monochromator (wavelength λ = 1.5543 Å) and a Cu(311) monochromator (λ = 1.5396 Å), respectively, on the 32-detector BT-1 diffractometer at the National Institute of Standards and Technology's research reactor. A figure containing the 50 K data with a fitted profile from Rietveld refinement is available at http://www.sciencemag.org/science/feature/beyond/#subramanian. The neutron sample was a pellet weighing 185 mg, which was loaded into a vanadium tube and positioned in the center of the neutron beam. For the 298 K neutron data set, aluminum in the sample mount was incompletely shielded. The resulting aluminum peaks were fit as a second phase with a Le Bail fit [A. Le Bail, H. Duroy, J. L. Fourquet, Mater. Res. Bull. 23, 447 (1988)]. At both temperatures, small peaks from vanadium scattering were also observed and were modeled as an additional phase.
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34. We thank Q. Z. Huang, M. K. Crawford, J. E. Greedan, A. C. Larson, and C. Broholm for useful discussions on the magnetic refinements, R. L. Harlow for help in the single-crystal work, and T. G. Calvarese and M. L. Plummer for help in the high-pressure synthesis. The work at Lawrence Liver-more was done under the auspices of the U.S. Department of Energy under contract W-7405-ENG-48. A.W.S. thanks NSF tor research grant DMR-9308530.