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β-Mn-Type Co8+xZn12–x as a Defect Cubic Laves Phase: Site Preferences, Magnetism, and Electronic Structure
Inorganic Chemistry
  • Weiwei Xie, Iowa State University
  • Srinvasa Timmaiah, Iowa State University
  • Jagat Lamal, Iowa State University
  • Jing Liu, Iowa State University
  • Thomas W. Heitmann, University of Missouri
  • Dante Quirinale, Iowa State University
  • A. I. Goldman, Iowa State University
  • Vitalij K. Pecharsky, Iowa State University
  • Gordon J. Miller, Iowa State University
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The results of crystallographic analysis, magnetic characterization, and theoretical assessment of β-Mn-type Co–Zn intermetallics prepared using high-temperature methods are presented. These β-Mn Co–Zn phases crystallize in the space group P4132 [Pearson symbol cP20; a = 6.3555(7)–6.3220(7)], and their stoichiometry may be expressed as Co8+xZn12–x [1.7(2) < x < 2.2(2)]. According to a combination of single-crystal X-ray diffraction, neutron powder diffraction, and scanning electron microscopy, atomic site occupancies establish clear preferences for Co atoms in the 8c sites and Zn atoms in the 12d sites, with all additional Co atoms replacing some Zn atoms, a result that can be rationalized by electronic structure calculations. Magnetic measurements and neutron powder diffraction of an equimolar Co:Zn sample confirm ferromagnetism in this phase with a Curie temperature of ∼420 K. Neutron powder diffraction and electronic structure calculations using the local spin density approximation indicate that the spontaneous magnetization of this phase arises exclusively from local moments at the Co atoms. Inspection of the atomic arrangements of Co8+xZn12–x reveals that the β-Mn aristotype may be derived from an ordered defect, cubic Laves phase (MgCu2-type) structure. Structural optimization procedures using the Vienna ab initio simulation package (VASP) and starting from the undistorted, defect Laves phase structure achieved energy minimization at the observed β-Mn structure type, a result that offers greater insight into the β-Mn structure type and establishes a closer relationship with the corresponding α-Mn structure (cI58).

Reprinted (adapted) with permission from Inorg. Chem., 2013, 52 (16), pp 9399–9408. Copyright 2013 American Chemical Society.

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Weiwei Xie, Srinvasa Timmaiah, Jagat Lamal, Jing Liu, et al.. "β-Mn-Type Co8+xZn12–x as a Defect Cubic Laves Phase: Site Preferences, Magnetism, and Electronic Structure" Inorganic Chemistry Vol. 52 Iss. 16 (2013) p. 9399 - 9408
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