Crystal and magnetic spin structure of Germanium-Hedenbergite, CaFeGe2O6, and a comparison with other magnetic/magnetoelectric/multiferroic pyroxenes

Günther J. Redhammer, Georg Roth, Anatoliy Senyshyn, Gerold Tippelt, and Clemens Pietzonka
  • 1 RWTH-Aachen, Institut für Kristallographie, Aachen, Deutschland
  • 2 Technische Universität München, Forschungneuronenquelle Heinz Maier-Leibnitz (FRM, Garching, Deutschland
  • 3 University of Salzburg, Department of Materials Engineering and Physics, Salzburg, Österreich
  • 4 Philipps-University Marburg, Fachbereich für Chemie, Marburg/Lahn, Deutschland

Abstract

CaFeGe2O6, the germanium-analogue to the mineral Hedenbergite, has been synthesized at 1273 K in evacuated SiO2-glass-tubes. Powder neutron diffraction data collected between 4 K and 300 K were used to evaluate the magnetic spin as well as the nuclear crystal structure and its T-evolution. CaFeGe2O6 is monoclinic, C2/c, a = 10.1778(5) Å, b = 9.0545(4) Å, c = 5.4319(3) Å, β = 104.263(3)°, Z = 4 at room temperature. No change of symmetry was observed down to 4 K. Below 43 K, additional magnetic Bragg reflections appear, which can be indexed on the basis of a commensurate magnetic propagation vector k [1, 0, 0]. The successful description of the magnetic spin structure reveals a ferromagnetic spin coupling within the Fe2+O6 M1 chains, while the coupling between the chains is antiferromagnetic. Spins are oriented collinearly within the ac plane and form an angle of ∼60° with the crystallographic a-axis. The magnetic moment at 4 K amounts to about 4.4 μB. The observed magnetic structure is similar to that of other Ca-clinopyroxenes. The present data are put into context with the structural and magnetic properties of other pyroxenes – among them magnetoelectric and multiferroic pyroxene-type compounds.

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