  Two dimensional van der Waals ferromagnets with honeycomb structures are
expected to host the bosonic version of Dirac particles in their magnon
excitation spectra. Using inelastic neutron scattering, we study spin wave
excitations in polycrystalline CrCl$_3$, which exhibits ferromagnetic honeycomb
layers with antiferromagnetic stackings along the $c$-axis. For comparison,
polycrystal samples of CrI$_3$ with different grain sizes are also studied. We
find that the powder-averaged spin wave spectrum of CrCl$_3$ at $T$ = 2 K can
be adequately explained by the two dimensional spin Hamiltonian including
in-plane Heisenberg exchanges only. The observed excitation does not exhibit
noticeable broadening in energy, which is in remarkable contrast to the
substantial broadening observed in CrI$_3$. Based on these results, we conclude
that the ferromagnetic phase of CrCl$_3$ hosts massless Dirac magnons and is
thus not topological.
