Unquenchedeg1orbital moment in the Mott-insulating antiferromagnetKOsO4

Abstract

Applying the correlated electronic structure method based on density functional theory plus Hubbard U interaction, we have investigated the tetragonal scheelite structure Mott insulator KOsO4, whose e 1 g configuration should be affected little by spin-orbit couping (SOC). The method reproduces the observed antiferromagnetic Mott insulating state, populating the Os d z 2 majority orbital. The quarter-filled eg manifold is characterized by a symmetry breaking due to the tetragonal structure, and the Os ion shows a crystal field splitting ∆ cf = 1.7 eV from the t2g complex, relatively small considering the high formal oxidation state Os 7+ . The small magnetocrystalline anisotropy before including correlation (i.e. in the metallic state) is increased by more than an order of magnitude in the Mott insulating state, a result of strong interplay between large SOC and strong correlation. In contrast to conventional wisdom that the eg complex will not support orbital magnetism, we find that for the easy axis [100] direction the substantial Os orbital moment ML ≈ −0.2µB that compensates half of the Os spin moment MS=0.4 µB. The origin of the orbital moment is analyzed and understood in terms of additional spin-orbital lowering of symmetry, beyond that due to structural distortion, for magnetization along [100]. Further interpretation is assisted by analysis of the spin density and the Wannier function with SOC included.

Frustrated Heisenberg $J_1-J_2$ model within the stretched diamond lattice of LiYbO2

“…It is unsurprising that the two magnetic interactions would be comparable in strength due to their relative superexchange pathways. In comparison, materials such as KRuO 4 [64] and KOsO 4 [65,66] share the same I4 1 /amd magnetic sublattice comprised of Ru and Os ions, but break the oxygenbased superexchange connection along J 2 . In these systems, magnetic order resides in the J 2 = 0 limit of the Heisenberg J 1 -J 2 model, where moments order within a Neél antiferromagnetic state and an unfrustrated J 1 [64][65][66].…”

Interplay between spin-orbit coupling and strong correlation effects: Comparison of the three osmate double perovskitesBa2AOsO6(A=Na, Ca, Y)

“…High valent osmates can have an open e g shell rather than t 2g shell. Song et al 13 have reported a theoretical study 13 of KOsO 4 with heptavalent Os, where large SOC, strong correlations, and structural symmetry breaking conspire to produce an unexpectedly large orbital moment in the e 1 g shell that nominally supports no orbital moment. The moment arises due to distortion from ideal tetrahedral symmetry of the ion, which allows mixing in of orbitals that support an orbital moment.…”

Emergent odd-parity multipoles and magnetoelectric effects on a diamond structure: Implication for the 5d transition metal oxides AOsO4(A=Hayami1, Kusunose2, Motome3 2018Phys. Rev. B410120View full textAdd to dashboardCite

“…This becomes relevant when the ratio λ/∆ c is not negligibly small (λ is the coupling constant of the atomic SOC). In fact, a relatively large value of λ/∆ c ∼ 0.18 was reported for KOsO 4 from the firstprinciples calculation 37 . When we take into account such a SOC effect in the second-order perturbation, the e g and t 2g levels are further split: the e g levels are lowered while keeping the fourfold degeneracy, whereas the t 2g levels are split into twofold and fourfold [see the rightmost panel in Fig.…”