Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Experimental determination of the magnetic interactions of frustrated
  Cairo pentagon lattice materials   We present inelastic neutron scattering measurements of the Cairo pentagon
lattice magnets Bi$_2$Fe$_4$O$_9$ and Bi$_4$Fe$_5$O$_{13}$F, supported by high
field magnetisation measurements of Bi$_2$Fe$_4$O$_9$. Using linear spin wave
theory and mean field analyses we determine the spin exchange interactions and
single-ion anisotropy in these materials. The Cairo lattice is geometrically
frustrated and consists of two inequivalent magnetic sites, both occupied by
Fe$^{3+}$ ions and connected by two competing nearest neighbour interactions.
We found that one of these interactions, coupling nearest neighbour spins on
the three-fold symmetric sites, is extremely strong and antiferromagnetic.
These strongly coupled dimers are then weakly coupled to a framework formed
from spins occupying the other inequivalent site. In addition we found that the
Fe$^{3+}$ $S=5/2$ spins have a non-negligible single-ion anisotropy, which
manifests as a spin anisotropy gap in the neutron spectrum and a spin-flop
transition in high field magnetisation measurements.

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The categories of this paper are: q-bio
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The categories of this paper are: eess
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The categories of this paper are: q-fin
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The categories of this paper are: stat
25
The categories of this paper are: patt-sol
9
The categories of this paper are: nlin
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The categories of this paper are: chao-dyn
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The categories of this paper are: gr-qc
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
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The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
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The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
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The categories of this paper are: physics
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The categories of this paper are: quant-ph