Magnetic excitations of XXZ-type honeycomb antiferromagnet Co_0.5Ni_0.5TiO₃

Honeycomb antiferromagnets are of great interest as potential hosts of Dirac magnons, spin-orbit excitons(SOEs), magnetic frustration, and related quantum magnetic phenomena. Co_xNi_1-xTiO₃ is a solid solution of CoTiO₃ and NiTiO₃ honeycomb antiferromagnets, where the two parent compounds exhibit rich quantum magnetic properties. CoTiO₃ is a topological system that exhibits XXZ- type exchange interactions and Dirac magnons, while isostructural NiTiO₃ exhibits more isotropic and Heisenberg-like exchange interactions with low energy magnons and magnetic frustration. We investigate the mixed system Co_0.5Ni_0.5TiO₃ (CNTO), which combines these two parent compounds with contrasting quantum magnetic behaviors. Neutron scattering measurements exhibits CNTO has an A-type magnetic ground state, undergoing antiferromagnetic ordering at Neel transition temperature ~ 27 K with an ordered magnetic moment 4.37 μ_B per magnetic ion. Inelastic neutron scattering exhibits well defined magnon excitations up to 13 meV and the SOEs above 15 meV. Linear spin wave theory calculations confirm the XXZ-type spin Hamiltonian. The mixed Co/Ni environment modifies magnon and spin-orbit exciton behavior compared to parent compounds, reflecting the role of chemical and spin disorder, spin orbit coupling and magnetic anisotropy shaping the magnetic excitation spectrum. These results show CNTO as a possible platform for tuning spin dynamics in honeycomb antiferromagnets with potential applications in magnonics.