Phase transitions and iron-ordered moment form factor in LaFeAsO

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2010-08-09
Authors
Li, H.-F.
Lograsso, Thomas
Tian, W.
Yan, J.-Q.
Zarestky, Jerel
McCallum, R.
Lograsso, Thomas
Vaknin, David
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Ames Laboratory
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Abstract

Elastic neutron-scattering studies of single-crystal LaFeAsO reveal that upon cooling, an onset of the tetragonal (T)-to-orthorhombic (O) structural transition occurs at TS≈156 K, and it exhibits a sharp transition at TP≈148 K. We argue that in the temperature range TS to TP, T and O structures may dynamically coexist possibly due to nematic spin correlations recently proposed for the iron pnictides, and we attribute TP to the formation of long-range O domains from the finite local precursors. The antiferromagnetic structure emerges at TN≈140 K, with the iron moment direction along the O a axis. We extract the iron magnetic form factor and use the tabulated ⟨j0⟩ of Fe, Fe2+, and Fe3+ to obtain a magnetic moment size of ∼0.8 μB at 9.5 K.

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This article is from Physical Review B 82 (2010): 064409, doi:10.1103/PhysRevB.82.064409.

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