Possibility of ferro-octupolar order in Ba${}_2$CaOsO${}_6$ assessed by X-ray magnetic dichroism measurements

Abstract

Localized $5d^2$ electrons in a cubic crystal field possess multipoles such as electric quadrupoles and magnetic octupoles. We studied the cubic double perovskite Ba${}_2$CaOsO${}_6$ containing the Os${}^{6+}$ ($5d^2$) ions, which exhibits a phase transition to a `hidden order' below $T^{\ast }\sim$ 50 K, by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at the Os $L_{2,3}$ edge. The cubic ligand-field splitting between the $t_{2g}$ and $e_g$ levels of Os $5d$ was deduced by XAS to be $\sim$4 eV. Ligand-field (LF) multiplet calculation under fictitious strong magnetic fields indicated that the exchange interaction between nearest-neighbor octupoles should be as strong as $\sim$1.5 meV if a ferro-octupolar order is stabilized in the `hidden-ordered' state, consistent with the exchange interaction of $\sim$1 meV previously predicted theoretically using model and density functional theory calculations. The temperature dependence of the XMCD spectra was consistent with a $\sim$18 meV residual cubic splitting of the lowest $J_{\mathrm{eff}}=$ 2 multiplet state into the non-Kramers $E_g$ doublet ground state and the $T_{2g}$ triplet excited state.

7 pages, 5 figures

References in corpus (19)

• Novel Jeff = 1/2 Mott State Induced by Relativistic Spin-Orbit Coupling in Sr2IrO4
• Strong electronic correlations from Hund's coupling
• Fermi Arcs in a Doped Pseudospin-1/2 Heisenberg Antiferromagnet
• Orbital effects in solids: basics, recent progress and opportunities
• A quantum liquid of magnetic octupoles on the pyrochlore lattice
• Proximate ferromagnetic state in the Kitaev model material $\alpha$-RuCl${}_3$
• Detection of multipolar orders in the spin-orbit-entangled 5d Mott insulator Ba2MgReO6
• The Jahn-Teller effect and spin--orbit coupling: friends or foes?
• Sleuthing out exotic quantum spin liquidity in the pyrochlore magnet Ce${}_2$Zr${}_2$O${}_7$
• Multipolar magnetism in d-orbital systems: Crystal field levels, octupolar order, and orbital loop currents
• Ferro-octupolar order and low-energy excitations in d${}^2$ double perovskites of Osmium
• Exchange interactions, Jahn-Teller coupling, and multipole orders in pseudospin one-half $5{\mathbf{d}}^2$ Mott insulators
• Anisotropic spin-density distribution and magnetic anisotropy of strained La${}_{1-x}$Sr${}_x$MnO${}_3$ thin films: Angle-dependent x-ray magnetic circular dichroism
• Probing octupolar hidden order via Janus impurities
• Signatures of hidden octupolar order from nonlinear Hall effects
• Effects of charge doping on Mott insulator with strong spin-orbit coupling, Ba${}_2$NaOsO${}_6$
• Spin-orbit-entangled electronic structure of Ba${}_2$CaOsO${}_6$ studied by O $K$-edge resonant inelastic X-ray scattering
• Resonant inelastic X-ray scattering investigation of Hund's and spin-orbit coupling in $5d^2$ double perovskites
• Second Harmonic Hall Response in Insulators: Inter-band Quantum Geometry and Breakdown of Kleinman's Conjecture