Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Influence of magnetic fields on the spin reorientation transition in
  ultra-thin films   The dependence of the spin reorientation transition in ultra-thin
ferromagnetic films on external magnetic fields is studied. For different
orientations of the applied field with respect to the film, phase diagrams are
calculated within a mean field theory for the classical Heisenberg model. In
particular we find that the spin reorientation transition present in this model
is not suppressed completely by an applied field, as the magnetization
component perpendicular to the field may show spontaneous order in a certain
temperature interval.

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The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
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The categories of this paper are: astro-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: chao-dyn
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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: nucl-ex
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con
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The categories of this paper are: nlin
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The categories of this paper are: q-bio
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The categories of this paper are: q-fin
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The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th