Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The low spin moment in LaOFeAs is due to a hidden multipole order caused
  by spin orbital ordering   An antiferro-magnetic (AF) low moment solution, 0.4 $\mu_\mathrm{B}$/Fe, is
found in the case of LaOFeAs for an intermediately strong Coulomb interaction
$U$ of 2.5--3.0 eV. This solution is stabilized over a large moment solution
due to the gain in exchange energy in the formation of large multipoles of the
spin magnetization density. The multipoles are of rank four and can be
understand as a kind of spin-orbital ordering. Parallels can be drawn to the
stabilization of the AF order in e.g. CaCuO$_2$.

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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
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The categories of this paper are: astro-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: plasm-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
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The categories of this paper are: adap-org
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: solv-int
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The categories of this paper are: cmp-lg
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The categories of this paper are: nlin