Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Thermodynamics of Heisenberg ferromagnets with arbitrary spin in a
  magnetic field   The thermodynamic properties (magnetization, magnetic susceptibility,
transverse and longitudinal correlation lengths, specific heat) of one- and
two-dimensional ferromagnets with arbitrary spin S in a magnetic field are
investigated by a second-order Green-function theory. In addition, quantum
Monte Carlo simulations for S= 1/2 and S=1 are performed using the stochastic
series expansion method. A good agreement between the results of both
approaches is found. The field dependence of the position of the maximum in the
temperature dependence of the susceptibility fits well to a power law at low
fields and to a linear increase at high fields. The maximum height decreases
according to a power law in the whole field region. The longitudinal
correlation length may show an anomalous temperature dependence: a minimum
followed by a maximum with increasing temperature. Considering the specific
heat in one dimension and at low magnetic fields, two maxima in its temperature
dependence for both the S= 1/2 and S = 1 ferromagnets are found. For S>1 only
one maximum occurs, as in the two-dimensional ferromagnets. Relating the theory
to experiments on the S= 1/2 quasi-one-dimensional copper salt TMCuC
[(CH_3)_4NCuCl_3], a fit to the magnetization as a function of the magnetic
field yields the value of the exchange energy which is used to make predictions
for the occurrence of two maxima in the temperature dependence of the specific
heat.

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The categories of this paper are: hep-ex
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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The categories of this paper are: cs
34
The categories of this paper are: chem-ph
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The categories of this paper are: stat
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The categories of this paper are: plasm-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: q-alg
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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: math
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-lat