beta-Mn-Type Co8+xZn12-x as a Defect Cubic Laves Phase: Site Preferences, Magnetism, and Electronic Structure

Titlebeta-Mn-Type Co8+xZn12-x as a Defect Cubic Laves Phase: Site Preferences, Magnetism, and Electronic Structure
Publication TypeJournal Article
Year of Publication2013
AuthorsXie WW, Thimmaiah S, Lamsal J, Liu J, Heitmann TW, Quirinale D, Goldman AI, Pecharsky V, Miller GJ
Journal TitleInorganic Chemistry
Date Published08
Type of ArticleArticle
ISBN Number0020-1669
Accession NumberWOS:000323460800028
Keywordsbrillouin-zone integrations, co-zn, crystal-structure, metal, quasi-crystal, symmetry, system, total-energy calculations, transition, wave basis-set

The results of crystallographic analysis, magnetic characterization, and theoretical assessment of, beta-Mn-type Co-Zn intermetallics prepared using high-temperature methods are presented. These beta-Mn Co-Zn phases crystallize in the space group P4(1)32 [Pearson symbol cP20; a = 6.3555(7)-6.3220(7)] and their stoichiometry may be expressed as Co8+zZn12-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 similar to 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 beta-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 beta-Mn structure type, a result that offers greater insight into the beta-Mn structure type and establishes a closer relationship with the corresponding alpha-Mn structure (cI58).

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