Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Double phase transition in the triangular antiferromagnet
  Ba$_3$CoTa$_2$O$_9$   Here, we report the synthesis and magnetic properties of a new triangular
lattice antiferromagnet Ba$_3$CoTa$_2$O$_9$. The effective spin of Co$^{2+}$ is
found to be $J=1/2$ at low temperatures due to the combined effect of crystal
field and spin-orbit coupling. Ba$_3$CoTa$_2$O$_9$ undergoes two successive
magnetic phase transitions at $T_{N1}\simeq0.70$~K and $T_{N2}\simeq0.57$~K in
zero applied field, which is typical for triangular antiferromagnets with the
easy-axis magnetic anisotropy. With increasing field, the transition anomalies
are found to shift toward low temperatures, confirming the antiferromagnetic
nature of the transitions. At higher fields, the transition peaks in the heat
capacity data disappear and give way to a broad maximum, which can be ascribed
to a Schottky anomaly due to the Zeeman splitting of spin levels. The $H-T$
phase diagram of the compound shows three distinct phases. The possible nature
of these phases is discussed.

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The categories of this paper are: physics
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The categories of this paper are: eess
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The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
33
The categories of this paper are: plasm-ph
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The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
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The categories of this paper are: math
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The categories of this paper are: supr-con
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The categories of this paper are: ao-sci
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The categories of this paper are: math-ph