  We report on a search for ultra-low-mass axion-like dark matter by analysing
the ratio of the spin-precession frequencies of stored ultracold neutrons and
$^{199}$Hg atoms for an axion-induced oscillating electric dipole moment of the
neutron and an axion-wind spin-precession effect. No signal consistent with
dark matter is observed for the axion mass range $10^{-24}~\textrm{eV} \le m_a
\le 10^{-17}~\textrm{eV}$. Our null result sets the first laboratory
constraints on the coupling of axion dark matter to gluons, which improve on
astrophysical limits by up to 3 orders of magnitude, and also improves on
previous laboratory constraints on the axion coupling to nucleons by up to a
factor of 40.
