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Nuclear and incommensurate magnetic structure of NaFeGe2O6 between 5 K and 298 K and new data on multiferroic NaFeSi2O6

The compound NaFeGe 2 O 6 was grown synthetically as polycrystalline powder and as large single crystals suitable for X-ray and neutron-diffraction experiments to clarify the low temperature evolution of secondary structural parameters and to determine the low temperature magnetic spins structure. N...

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Bibliographic Details
Published in:Physics and chemistry of minerals 2011-02, Vol.38 (2), p.139-157
Main Authors: Redhammer, Günther J., Senyshyn, Anatoliy, Meven, Martin, Roth, Georg, Prinz, Sebastian, Pachler, Astrid, Tippelt, Gerold, Pietzonka, Clemens, Treutmann, Werner, Hoelzel, Markus, Pedersen, Björn, Amthauer, Georg
Format: Article
Language:English
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Summary:The compound NaFeGe 2 O 6 was grown synthetically as polycrystalline powder and as large single crystals suitable for X-ray and neutron-diffraction experiments to clarify the low temperature evolution of secondary structural parameters and to determine the low temperature magnetic spins structure. NaFeGe 2 O 6 is isotypic to the clinopyroxene-type compound aegirine and adopts the typical H T - C 2/ c clinopyroxene structure down to 2.5 K. The Na-bearing M2 polyhedra were identified to show the largest volume expansion between 2.5 K and room temperature, while the GeO 4 tetrahedra behave as stiff units. Magnetic susceptibility measurements show a broad maximum around 33 K, which marks the onset of low-dimensional magnetic ordering. Below 12 K NaFeGe 2 O 6 transforms to an incommensurately modulated magnetic spin state, with k  = [0.323, 1.0, 0.080] and a helical order of spins within the M1-chains of FeO 6 octahedra. This is determined by neutron-diffraction experiments on a single crystal. Comparison of NaFeGe 2 O 6 with NaFeSi 2 O 6 is given and it is shown that the magnetic ordering in the latter compound, aegirine, also is complex and is best described by two different spin states, a commensurate one with C 2′/ c ′ symmetry and an incommensurate one, best being described by a spin density wave, oriented within the (1 0 1) plane.
ISSN:0342-1791
1432-2021
DOI:10.1007/s00269-010-0390-3