  SmN is a ferromagnetic semiconductor with the unusual property of an
orbital-dominant magnetic moment that is largely cancelled by an antiparallel
spin contribution, resulting in a near-zero net moment. However, there is a
basic gap in the understanding of the ferromagnetic ground state, with existing
density functional theory calculations providing values of the $4f$ magnetic
moments at odds with experimental data. To clarify the situation, we employ an
effective $4f$ Hamiltonian incorporating spin-orbit coupling, exchange, the
crystal field, and $J$-mixing to calculate the ground state $4f$ moments. Our
results are in excellent agreement with experimental data, revealing moderate
quenching of both spin and orbital moments to magnitudes of $\sim 2~\mu_B$ in
bulk SmN, enhanced to an average of $\sim 3~\mu_B$ in SmN layers within a
SmN/GdN superlattice. These calculations provide insight into recent studies of
SmN showing that it is an unconventional superconductor at low temperatures and
displays twisted magnetization phases in magnetic heterostructures.
