Disentangling orbital and spin exchange interactions for Co${}^{2+}$ on a rocksalt lattice

Abstract

Neutron spectroscopy was applied to study the magnetic interactions of orbitally degenerate Co${}^{2+}$ on a host MgO rocksalt lattice where no long range spin or orbital order exists. The paramagnetic nature of the substituted monoxide Co${}_{0.03}$Mg${}_{0.97}$O allows for the disentanglement of spin-exchange and spin-orbit interactions. By considering the prevalent excitations from Co${}^{2+}$ spin pairs, we extract 7 exchange constants out to the fourth coordination shell. An antiferromagnetic next nearest neighbor 180${}^{\circ }$ exchange interaction is dominant, however dual ferromagnetic and antiferromagnetic interactions are observed for pairings with other pathways. These interactions can be understood in terms of a combination of orbital degeneracy in the $t_{2g}$ channel and the Goodenough-Kanamori-Anderson (GKA) rules. Our work suggests that such a hierarchy of exchange interactions exists in transition metal-based oxides with a $t_{2g}$ orbital degeneracy.

arXiv comment(main text - 7 pages, 3 figures, 1 table; supplementary information - 6 pages, 3 figures, 2 tables, to be published in Physical Review B)

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• Magnetic Couplings in Edge-Sharing High-Spin $d^7$ Compounds
• Towards Kitaev Spin Liquid in 3d Transition Metal Compounds
• Spin-Orbit Excitons in CoO
• Two-dimensional ferromagnetic spin-orbital excitations in the honeycomb VI${}_3$
• Ordered magnetism in the intrinsically decorated $j{}_{\mathrm{eff}}$ = $\frac{1}{2}$ $\alpha$-CoV${}_3$O${}_8$
• Van Vleck excitons in Ca${}_2$RuO${}_4$
• Magnetic Fluctuations and the Spin-Orbit Interaction in Mott Insulating CoO
• Absence of moment fragmentation in the mixed $B$-site pyrochlore Nd${}_2$GaSbO${}_7$
• Diffusive Excitonic Bands from Frustrated Triangular Sublattice in a Singlet-Ground-State System
• Relaxing Kondo screened Kramers-doublets in CeRhSi${}_3$
• Zeeman split Kramers doublets in spin-supersolid candidate Na${}_2$BaCo(PO${}_4$)${}_2$
• Spin-orbital correlations from complex orbital order in MgV${}_2$O${}_4$
• Metastable and localized Ising magnetism in $\alpha$-CoV${}_2$O${}_6$ magnetization plateaus
• Excitonic transverse and amplitude fluctuations in the noncollinear and charge-ordered RbFe${}^{2+}$Fe${}^{3+}$F${}_6$
• Anisotropic excitonic magnetism from discrete ${\mathrm{C}}_4$ symmetry in CeRhIn${}_5$
• Anisotropic Band-Split Magnetism in Magnetostrictive CoFe${}_2$O${}_4$
• X-raying Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O: disentangling elemental contributions in a prototypical high-entropy oxide