Magnetic Behavior of Superconductor 2H-NbSe2 Intercalated with Iron: First Principle Study

Abstract

We investigated the structural, electronic and magnetic properties of iron-intercalated niobium selinium, $Fe_{x}NbSe_{2}$ for $x = 0$ and 0.25, from first principle calculations. The tendency towards the localization in superconductors criterion which has been extracted from our results placed the $NbSe_{2}$ compound in vicinity of Fe-based superconductors. The DFT plus on-site coulomb repulsion U (DFT+U) and the exact exchange for correlated electrons (DFT+EECE)-based hybrid functional were used including the spin-orbit coupling (SOC) to understand the role of correlation and SOC effects in this type of systems. The calculation predicts the correct antiferromagnetic (AF) ground state, from both the generalized gradient approximation (GGA) and GGA+U. A shift up in the Fermi energy was observed after the intercalation of 2H-NbSe2 with iron, indicating a charge transfer from Fe to the host compound. The obtained magnetic moment of Fe is enhanced by a correlation effect in both DFT+U and DFT+EECE over the small value from GGA-only. Moreover, a large unquenched orbital magnetic moment is saturated to $m_{orb} \sim 0.6\mu _{B}$ under a moderate correlation effect of $U_{eff}\sim 2.0eV$ . We also show that the correlation effect is important along side with SOC in order to get a true picture for the band filling consistent with that of the crystal field splitting and a large unquenched $m_{orb}$ which has been found experimentally in such systems. Therefore, the combination of correlation and SOC effects is a decisive choice for further studies of such systems.