Nuclear and incommensurate magnetic structure of NaFeGe2O6 between 5聽K and 298聽K and new data on multiferroic NaFeSi2O6
| 详细信息 | 推荐本文 | |
- 作者：G眉nther J. Redhammer (1) Guenther.redhammer@sbg.ac.at
Anatoliy Senyshyn (23)
Martin Meven (2)
Georg Roth (4)
Sebastian Prinz (4)
Astrid Pachler (1)
Gerold Tippelt (1)
Clemens Pietzonka (5)
Werner Treutmann (6)
Markus Hoelzel (23)
Bj枚rn Pedersen (2)
Georg Amthauer (1) - 关键词：Clinopyroxene – ; NaFeGe2O6 – ; Aegirine NaFeSi2O6 – ; Multiferroic compounds – ; Neutron diffraction – ; Magnetic ordering – ; Helical spin structure
- 刊名：Physics and Chemistry of Minerals
- 出版时间：February 2011
- 出版年：2011
- 期刊代码：117_0342-1791
- 类别：ear
- 卷：38
- 期：2
- 页码：139-157
- 数据来源：sp
摘要
The compound NaFeGe2O6 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. NaFeGe2O6 is isotypic to the clinopyroxene-type compound aegirine and adopts the typical HT-C2/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 GeO4 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 NaFeGe2O6 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 FeO6 octahedra. This is determined by neutron-diffraction experiments on a single crystal. Comparison of NaFeGe2O6 with NaFeSi2O6 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 C2′/c′ symmetry and an incommensurate one, best being described by a spin density wave, oriented within the (1 0 1) plane.