Large orbital moment and spin-orbit enabled Mott transition in the Ising Fe honeycomb lattice BaFe2(PO4)2

Abstract

BaFe2(PO4)2 is an unusual Ising insulating ferromagnet based on the Fe${}^{2+}$ spin $S$ = 2 ion, the susceptibility of which suggests a large orbital component to the Fe local moment. We apply density functional theory based methods to obtain a microscopic picture of the competing interactions and the critical role of spin-orbit coupling (SOC) in this honeycomb lattice system. The low-temperature ferromagnetic phase displays a half-semimetallic Dirac point pinning the Fermi level and preventing gap opening before consideration of SOC, presenting a case in which correlation effects modeled by a repulsive Hubbard $U$ fail to open a gap. Simultaneous inclusion of both correlation and SOC drives a large orbital moment in excess of 0.7 ${\mu }_B$ (essentially $L$ = 1) for spin aligned along the $\hat{c}$ axis, with a gap comparable with the inferred experimental value. The large orbital moment accounts for the large Ising anisotropy, in spite of the small magnitude of the SOC strength on the 3$d$ (Fe) ion. Ultimately, the Mott-Hubbard gap is enabled by degeneracy lifting by SOC and the large Fe moments, rather than by standard Hubbard interactions alone. We suggest that competing orbital occupations are responsible for the structural transitions involved in the observed re-entrant rhombohedral-triclinic-rhombohedral sequence.

6+ pages, 5 figures

References in corpus (12)

• Theoretical Discovery/Prediction: Weyl Semimetal states in the TaAs material (TaAs, NbAs, NbP, TaP) class
• Weyl semimetal phase in non-centrosymmetric transition metal monophosphides
• Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal NbP
• Quantum spin Hall effect in a transition metal oxide Na2IrO3
• Origin of the Structural and Magnetic Anomaly of the Layered Compound SrFeO2: A Density Functional Investigation
• sd2 Graphene: Kagome Band in Hexagonal lattice
• Confinement-driven transitions between topological and Mott phases in (LaNiO3)${}_N$/(LaAlO3)${}_M$(111) superlattices
• Orbital-quenching-induced magnetism in Ba_2NaOsO_6
• Spin-orbit coupling, strong correlation, and insulator-metal transitions: the J${}_{\mathrm{eff}}$ =3\2 ferromagnetic Mott insulator Ba${}_2$NaOsO${}_6$
• First Principles Study of the Electronic and Vibrational Properties of LiNbO2
• Spontaneous formation of kagome network and Dirac half-semimetal on a triangular lattice
• Strain and Spin-Orbit Coupling Induced Orbital-Ordering in Mott Insulator BaCrO3

Cited by in corpus (9)

• Realizing Haldane Model in Fe-based Honeycomb Ferromagnetic Insulators
• Spin orientations of the spin-half Ir4+ ions in Sr3NiIrO6, Sr2IrO4 and Na2IrO3: Density functional, perturbation theory and Madelung potential analyses
• Tuning ferromagnetic BaFe${}_2$(PO${}_4$)${}_2$ through a high Chern number topological phase
• Confinement-driven electronic and topological phases in corundum-derived $3d$-oxide honeycomb lattices
• Influence of graphene on the electronic and magnetic properties of an iron(III) porphyrin chloride complex
• Molecular orbital polarization in Na2Ti2Sb2O: microscopic route to metal-metal transition without spontaneous symmetry breaking
• Band crossings in honeycomb-layered transition metal compounds
• Interaction-driven spin-orbit effects and Chern insulating phases in corundum-based $4d$ and $5d$ oxide honeycomb lattices
• Design of Chern Insulating Phases in Honeycomb Lattices