Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Intrinsic magnetic properties of NdFeAsO$_{0.9}$F$_{0.1}$ superconductor
  from local and global measurements   Magneto-optical imaging was used to study the local magnetization in
polycrystalline NdFeAsO$_{0.9}$F$_{0.1}$ (NFAOF). Individual crystallites up to
$\sim200\times100\times30$ $\mu m^{3}$ in size could be mapped at various
temperatures. The in-grain, persistent current density is about $j\sim10^{5}$
A/cm$^{2}$ and the magnetic relaxation rate in a remanent state peaks at about
$T_{m}\sim38$ K. By comparison with with the total magnetization measured in a
bar-shaped, dense, polycrystalline sample, we suggest that
NdFeAsO$_{0.9}$F$_{0.1}$ is similar to a layered high-$T_{c}$, compound such as
Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ and exhibits a $3D\to2D$ crossover in the
vortex structure. The 2D Ginzburg parameter is about $Gi^{2D}% \simeq10^{-2}$
implying electromagnetic anisotropy as large as $\epsilon \sim1/30$. Below
$T_{m}$, the static and dynamic behaviors are consistent with collective
pinning and creep.

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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: funct-an
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The categories of this paper are: quant-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: math
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The categories of this paper are: q-alg
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-th
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The categories of this paper are: physics
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The categories of this paper are: econ
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The categories of this paper are: gr-qc
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: stat