  We report on the magnetic properties of monovacancy defects in
neutron-irradiated graphite, probed by $^{13}$C nuclear magnetic resonance
spectroscopy. The bulk paramagnetism of the defect moments is revealed by the
temperature dependence of the NMR frequency shift and spectral linewidth, both
of which follow a Curie behavior, in agreement with measurements of the
macroscopic magnetization. Compared to pristine graphite, the fluctuating
hyperfine fields generated by the defect moments lead to an enhancement of the
$^{13}$C nuclear spin-lattice relaxation rate $1/T_{1}$ by about two orders of
magnitude. With an applied magnetic field of 7.1 T, the temperature dependence
of $1/T_{1}$ below about 10 K can well be described by a thermally activated
form, $1/T_{1}\propto\exp(-\Delta/k_{B}T)$, yielding a singular Zeeman energy
of ($0.41\pm0.01$) meV, in excellent agreement with the sole presence of
polarized, non-interacting defect moments.
