Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spin wave excitations in the tetragonal double perovskite Sr$_2$CuWO$_6$   Sr$_2$CuWO$_6$ is a double perovskite proposed to be at the border between
two and three dimensional magnetism, with a square lattice of $S=\frac{1}{2}$
Cu$^{2+}$ ions. We have used inelastic neutron scattering to investigate the
spin wave excitations of the system, to find out how they evolve as a function
of temperature, as well as to obtain information about the magnetic exchange
interactions. We observed well defined dispersive spin wave modes at $6$~K,
which partially survive above the magnetic ordering temperature, $T_N=24$~K.
Linear spin wave theory is used to determine the exchange interactions
revealing them to be highly two-dimensional in nature. Density functional
theory calculations are presented supporting this experimental finding, which
is in contrast to a previous \emph{ab-initio} study of the magnetic
interactions. Our analysis confirms that not the nearest neighbour, but the
next nearest neighbour interactions in the tetragonal $ab$ plane are the
strongest. Low incident energy measurements reveal the opening of a
$0.6(1)$~meV gap below $T_N$, which suggests the presence of a very weak single
ion anisotropy term in the form of an easy axis along $\hat{\mathbf{a}}$.

20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
18
The categories of this paper are: econ
17
The categories of this paper are: q-fin
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol