Emergence of exotic electronic and magnetic phases upon electron filling in NaBO (B = Ta, Ir, Pt, and Tl): a first-principles study.

Competition between spin-orbit interaction and electron correlations can stabilize a variety of non-trivial electronic and magnetic ground states. Using density functional theory calculations, here we show that different exotic electronic and magnetic ground states can be obtained by electron filling of the B-site cation in the NaBO family of compounds (B = Ta, Ir, Pt and Tl). Electron filling leads to a Peierls insulator state with a direct band gap to = 1/2 spin-orbit assisted Mott-insulator to band insulator and then to negative charge-transfer half-metal transition. The magnetic ground state also undergoes a transition from a non-magnetic state to a zigzag antiferromagnetic state, a re-entrant non-magnetic state and finally to a ferromagnetic state. The electron localization function shows a ladder type dimerization or Peierls instability in NaTaO. Maximally localized Wannier function calculations reveal delocalization of electrons through the e orbitals, which form a π bond, and localization of electrons through the t orbitals, which form a σ bond, between the neighbouring tantalum ions. NaTlO shows Stoner or band ferromagnetism due to the localized moments with up-spin on oxygen ligands created by the negative charge-transfer character, interacting the down-spin itinerant electrons of the Tl 5d-O 2p hybridized band. These findings are significant for practical applications; for instance the direct band gap insulator NaTaO shows potential for utilisation in solar cells, while NaTlO, which exhibits ferromagnetic half metallicity, holds promise for spintronic device applications.