On the ferromagnetic ground state of SmN

TL;DR

This paper clarifies the ferromagnetic ground state of SmN by employing an effective Hamiltonian approach, resolving discrepancies with experimental data and providing insights into its magnetic and superconducting properties.

Contribution

It introduces an effective 4f Hamiltonian including spin-orbit, exchange, crystal field, and J-mixing to accurately calculate SmN's ground state moments, aligning theory with experiments.

Findings

Calculated 4f moments of ~2 μ_B in bulk SmN

Enhanced moments of ~3 μ_B in SmN layers within superlattices

Provided insights into SmN's unconventional superconductivity and twisted magnetization phases

Abstract

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.