Peculiar role of f-orbital occupancy in heavy-fermion antiferromagnetic CeNMSb2 (NM: Cu and Au) compounds

•Role of 4f orbitals for the determination of magnetic ground state of CeCuSb2 and CeAuSb2 is elucidated.•Spin-polarized calculation with both spin-orbit coupling and LDA + U method can correctly predict the magnetic ground state.•Spin-density plots show that the effect of spin-orbit coupling of Ce plays a more crucial role than that for other atoms.•Different occupations of 4f-orbitals of Ce in CeNMSb2 compounds lead to the different orientations of magnetic easy axes.

We investigated the electronic structures of antiferromagnetic (AFM) CeNMSb2 (NM = Cu and Au) by using the full-potential linearized-augmented-plane-wave method to clarify the role of 4f electrons in determining the ground state. Total-energy differences show that it is necessary to include both spin-orbit coupling (SOC) and the so-called LDA + U method in the spin-polarized calculation to predict the correct magnetic easy axis for AFM CeNMSb2 compounds. The spin density, density of states and SOC energy calculated by using l ⋅ s matrix elements of f-orbitals indicate that the effects of SOC of Ce atom, especially the Ce 4f electrons, play a crucial role to determine the magnetic easy axes of these systems. The on-site Coulomb interaction of Ce atom is also very important.