Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Uniform Magnetic Order in a Ferromagnetic-Antiferromagnetic Random
  Alternating Quantum Spin Chain   An $S=1/2$ ferromagnetic (F) - antiferromagnetic (AF) random alternating
Heisenberg quantum spin chain model is investigated in connection to its
realization compound: (CH$_3$)$_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x}$)$_3$. The
exchange interaction bonds have alternating strong F-AF random bonds and weak
uniform AF bonds. Using the quantum Monte Carlo method we have found that the
excitation energy gap closes and the uniform AF order becomes critical in the
intermediate concentration region. This finding explains the experimental
observation of the magnetic transition by considering weak interchain
interactions. Present results suggest that the uniform AF order survives even
in the presence of randomly located ferromagnetic bonds. This may be a new
quantum effect.

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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
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The categories of this paper are: adap-org
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The categories of this paper are: eess
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The categories of this paper are: hep-lat
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The categories of this paper are: patt-sol
3
The categories of this paper are: physics
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
2
The categories of this paper are: math
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The categories of this paper are: ao-sci
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The categories of this paper are: stat
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The categories of this paper are: math-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-alg
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The categories of this paper are: nucl-ex