Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fluctuations and correlations in a frustrated S=1/2 square lattice with
  competing ferromagnetic and antiferromagnetic interactions: a muSR study   Zero and longitudinal field $\mu$SR measurements in Pb$_2$VO(PO$_4$)$_2$ and
BaCdVO(PO$_4$)$_2$, two prototypes of the frustrated $S=1/2$ square lattice
model with competing ferromagnetic and antiferromagnetic interactions, are
presented. Both systems are observed to undergo a phase transition to a
long-range magnetic order at $T_N\simeq 3.46$ K, for Pb$_2$VO(PO$_4$)$_2$, and
at $T_N\simeq 0.99$ K, for BaCdVO(PO$_4$)$_2$. In Pb$_2$VO(PO$_4$)$_2$ both the
temperature dependence of the order parameter and the longitudinal relaxation
rate above $T_N$ are consistent with a two-dimensional XY model. On the other
hand, for BaCdVO(PO$_4$)$_2$, which lies very close to the magnetically
disordered region of the phase diagram where a bond-nematic order was
predicted, a peculiar logarithmic increase of the relaxation is observed above
$T_N$. In both systems a rather broad distribution of internal fields at the
muon sites is noticed below $T_N$. The origin of this distribution is discussed
in the light of the $\mu$SR experiments already performed on $S=1/2$ frustrated
antiferromagnets on a square lattice.

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The categories of this paper are: physics
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The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci
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The categories of this paper are: eess
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The categories of this paper are: hep-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: nlin
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The categories of this paper are: math
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The categories of this paper are: gr-qc
14
The categories of this paper are: math-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: econ
12
The categories of this paper are: nucl-th