Spin-Orbit-Entangled Magnetic Excitations in the Quasi-1D Spin-Chain Compound Sr₆Rh₅O₁₅ Probed by Inelastic Neutron Scattering

4d transition-metal oxides display diverse magnetic ground states arising from the interplay of crystal-field effects, electronic correlations, and spin orbit coupling (SOC). In 4d systems, extended orbitals enhance covalency and bandwidth, while moderate SOC can stabilize spin orbit entangled Jeff states. Magnetism in this regime originates from anisotropic pseudospins rather than purely spin-only moments.
Sr6Rh5O15 is a quasi-one-dimensional mixed-valence rhodium oxide where Rh ions form chains along the c-axis with alternating octahedral and trigonal prismatic coordination. Octahedral Rh4+(4d5) ions can host Jeff=1/2 moments, while trigonal-prismatic Rh3+(4d6) ions may retain finite orbital contributions due to incomplete quenching. The coexistence of these inequivalent SOC-active sites creates a strongly anisotropic, spin orbit entangled magnetic lattice.
Dc magnetization shows long-range ordering near 11K with CW = -78 K, indicating dominant AFM interactions. The reduced effective moment (2.98 B/f.u.) compared to the free-ion value suggests strong SOC and covalency. M-H reveal butterfly-shaped hysteresis with distinct slope changes and small symmetric loops around 2T.
To clarify the microscopic origin of these properties, inelastic neutron scattering (INS) is crucial. INS will probe the spin-excitation spectrum, determine the nature and strength of Rh-Rh exchange interactions, and establish the magnetic energy scales governing this quasi-1D SOC-driven system.