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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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Published in: | Physics and chemistry of minerals 2011-02, Vol.38 (2), p.139-157 |
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Main Authors: | , , , , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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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. |
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ISSN: | 0342-1791 1432-2021 |
DOI: | 10.1007/s00269-010-0390-3 |