Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ferromagnetic phase of a uniaxial magnet with anisotropic biquadratic
  exchange   The ferromagnetic phase (FMP) of a uniaxial magnet with the easy-plane
single-ion anisotropy (SIA) and the anisotropic biquadra\-tic exchange
interaction (BQEI) has been studied. The case $S=1$ for the site spin $S$ has
been considered. Expressions for two branches of the spin excitation spectrum
at finite temperatures $T$ have been obtained, and the conditions for spectral
mode stability have been determined. The spectral mode stability diagram in the
$T-h$ coordinates has been constructed. The diagram testifies that, under
certain conditions, the temperature decrease is accompanied by a violation of
the spectral mode stability followed, as the temperature decreases further, by
its restoration; i.e. the reentrance phenomenon is observed. The temperature of
the second-order phase transition (PT) from the FMP into the phase with
spontaneously broken symmetry has been demonstrated to depend considerably on
the BQEI anisotropy constant.

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The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
2
The categories of this paper are: math
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The categories of this paper are: mtrl-th
16
The categories of this paper are: stat
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The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
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The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
10
The categories of this paper are: q-bio