  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.

Materials Science