Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spindynamics in the antiferromagnetic phases of the Dirac metals
  $A$MnBi$_2$ ($A=$ Sr, Ca)   The square Bi layers in $A$MnBi$_2$ ($A =$ Sr, Ca) host Dirac fermions which
coexist with antiferromagnetic order on the Mn sublattice below $T_\mathrm{N} =
290\,$K (Sr) and $270\,$K (Ca). We have measured the spin-wave dispersion in
these materials by triple-axis neutron spectroscopy. The spectra show
pronounced spin gaps of 10.2(2)$\,$meV (Sr) and 8.3(8)$\,$meV (Ca) and extend
to a maximum energy transfer of 61 - 63$\,$meV. The observed spectra can be
accurately reproduced by linear spin-wave theory from an Heisenberg effective
spin Hamiltonian. Detailed global fits of the full magnon dispersion are used
to determine the in-plane and inter-layer exchange parameters as well as on the
magnetocrystalline anisotropy constant. To within experimental error we find no
evidence that the magnetic dynamics are influenced by the Dirac fermions.

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The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
10
The categories of this paper are: q-bio
3
The categories of this paper are: physics