Magnetic ground state and excitations in the mixed 3d-4d quasi-one-dimensional spin-chain oxide Sr3NiRhO6

Entanglement of spin and orbital degrees of freedom, via relativistic spin-orbit coupling, in 4d transition metal oxides can give rise to a variety of unique quantum phases. A previous study of mixed 3d-4d quasi-1D spin-chain oxide Sr3NiRhO6 using the magnetization measurements by Mohapatra et al. [Phys. Rev. B 75 , 214422 (2007)] revealed a partially disordered antiferromagnetic structure below 50 K. We here report the magnetic ground state and spin-wave excitations in Sr3NiRhO6 using muon spin rotation and relaxation (mu SR), and neutron (elastic and inelastic) scattering techniques. Our neutron diffraction study reveals that in the magnetic structure of Sr3NiRhO6 Rh4+ and Ni2+ spins are aligned ferromagnetically in a spin chain, with moments along the crystallographic c axis. However, spin chains are coupled antiferromanetically in the ab plane. mu SR reveals the presence of oscillations in the asymmetry-time spectra below 50 K, supporting the long-range magnetically ordered ground state. Our inelastic neutron scattering study reveals gapped quasi-1D magnetic excitations with a large ratio of gap to exchange interaction. The observed spin-wave spectrum could be well fitted with a ferromagnetic isotropic exchange model (with J = 3.7 meV) and single ion anisotropy (D = 10 meV) on the Ni2+ site. The magnetic excitations survive up to 85 K, well above the magnetic ordering temperature of similar to 50 K, also indicating a quasi-1D nature of the magnetic interactions in Sr3NiRhO6.