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Stabilization of a Metastable Fibrous Bi21.2(1)(Mn1-xCox)20Phase with Pseudo-Pentagonal Symmetry Prepared Using a Bi Self-Flux

  • Author(s): Thimmaiah, S
  • Taufour, V
  • Saunders, S
  • March, S
  • Zhang, Y
  • Kramer, MJ
  • Canfield, PC
  • Miller, GJ
  • et al.

A new phase Bi21.2(1)(Mn1-xCox)20 (x-0.15) that was discovered during systematic substitution of 3d and 4d transition metals for Mn in LT-BiMn (NiAs-type) was reported as a theoretically predicted strategy to increase magnetic anisotropy and stabilization of NiAs-type structure at elevated temperature. Crystals of a new metastable Co-doped BiMn phase were grown using Bi as a self-flux at 280°C. The crucible with the elements was sealed in a fused silica ampule under an argon atmosphere, which was then heated to 1150°C, held at 1150 °C for 5 h, and then cooled to 390°C over 5 h. Samples were kept at 390°C for 2 h, and then cooled at a rate of approximately 1°C per hour to 280°C. Once the temperature was stabilized at 280°C, the excess Bi was removed by centrifugation. X-ray powder diffraction data were collected on a Rigaku Miniflex diffractrometer operating in a Bragg-Brentano geometry using Cu Kα radiation at room temperature. Because of the soft nature of product, the crystals were immersed in liquid nitrogen for a few minutes before grinding into powder. An empirical absorption correction was applied using the program SADABS. Total energy calculations using VASP revealed that no chemical ordering of cobalt occurs in that structure, i.e., Co is randomly distributed on the Mn sites, and that low-temperature magnetic ordering is possible.

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