Acta Crystallographica Section B

Structural Science

Volume 63, Part 5 (October 2007)

research papers

Acta Cryst. (2007). B63, 703-712 [ doi:10.1107/S0108768107038104 ]

Hexagonal ferrites: a unified model of the (TS)_nT series in superspace

I. Orlov, L. Palatinus, A. Arakcheeva and G. Chapuis

Abstract: Hexagonal ferrites represent an extensive family of mixed-layer magnetic materials with periods up to 1500 Å along the stacking direction, probably constituting the largest unit cells in the inorganic realm. The (TS)_nT subfamily includes $P\bar{3}m1$ and $R\bar{3}m$ structures that can be derived from Y ferrite Ba₂M₂Fe₁₂O₂₂ (M = Zn, Fe, Co, Mg, Mn) by introducing stacking faults. A unified (3 + 1)-dimensional superspace model is proposed for all members of the (TS)_nT family. The model belongs to the superspace group $X\bar{3}m1(00\gamma)$ with $\textstyle X = \{\left({{1}\over{3}},{{2}\over{3}},0,{{1}\over{3}}\right)$ , $\textstyle\left({{2}\over{3}},{{1}\over{3}},0,{{2}\over{3}}\right)\}$ , has a unit cell of the basic structure with a = 5.88, c = 4.84 Å and modulation vector ${\bf q} = {{4n+3}\over{9n+6}}{\bf c}^*$ , where n is rational for periodic structures and irrational for the aperiodic ones. The model was tested on calculated data of one of the principal members of the (TS)_nT family, the Y ferrite ( $n = \infty$ ). The fit obtained with the superspace model was excellent. The model allowed a reduction of refinable parameters by 19% with respect to the ordinary refinement without a significant increase of the refinement R values.

Keywords: hexagonal ferrites; superspace model; mixed-layer magnetic materials.


	Text file (4.9 kbytes) [ doi:10.1107/S0108768107038104/sn5054sup1.txt ] Supplementary material

	Text file (5.5 kbytes) [ doi:10.1107/S0108768107038104/sn5054sup2.txt ] Supplementary material

	Text file (26.0 kbytes) [ doi:10.1107/S0108768107038104/sn5054sup3.txt ] Supplementary material

	Text file (1.0 kbytes) [ doi:10.1107/S0108768107038104/sn5054sup4.txt ] Supplementary material

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