An X-ray, Mössbauer and magnetization investigation of hexagonal FeSe

Amcoff, T. Ericsson, A. Gismelseed

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

X-ray diffraction (XRD), Mössbauer spectroscopy (MS), and magnetization (SQUID) data are reported for a “pyrrhotite-like” compound (∂-FeSe), belonging to the central portion of the FeSe system. The ∂-phase(s) extends compositionally over a range of around Feo.94Se-Feo.86Se at 870 K, but narrows around Fe7Se8 at room temperature. Lattice parameters for the primitive hexagonal cell decrease regularly with increasing vacancy concentration x in Fe1-.xSe; c = 5.97 — 5.87 A, a = 3.65 — 3.62 A. An observed regular decrease in cell axes ratio, c/a = 1.644 — 0.145 x, is described as due to increased ordering with increased vacancy concentration. The disordered high-temperature 1 c structure is maintained at room temperature for vacancy-poor compositions, while superstructures, 3c and 4c, form for vacancy-rich compositions. Using a bond model for the magnetic coupling, MS spectra for ordered 3c and 4c superstructures can be well fitted assuming three well-defined surroundings, while those for disordered lc show a distribution in surroundings. A spin direction change, from the c-plane towards the c-axis with decrease in temperature, is sharp at 130 K for 3c, extended and incomplete for 4c (~220 — 120 K), and again rather sharp for lc at ∽ 220 K. It is suggested that the spin flip at 130 K for 3c, which is also visible (but weak) in SQUID measurements of lc samples, is indicative of an element of short range order in the disordered structure.

Original languageEnglish
Pages (from-to)197-205
Number of pages9
JournalZeitschrift fur Kristallographie - New Crystal Structures
Volume209
Issue number3
DOIs
Publication statusPublished - 1994

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Inorganic Chemistry

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