Microscopic investigation of spin dynamics in the single-chain magnet Sr4Mn2CoO9

G. Roy; S. Ghosh; M. Kumar; E. Kushwaha; J. Sannigrahi; V. Caignaert; W. Prellier; D. T. Adroja; D. Voneshen; V. Hardy; T. Basu

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arXiv · 2608.14222

Microscopic investigation of spin dynamics in the single-chain magnet Sr4Mn2CoO9

G. Roy·S. Ghosh·M. Kumar·E. Kushwaha·J. Sannigrahi·V. Caignaert·W. Prellier·D. T. Adroja·D. Voneshen·V. Hardy·T. Basu

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Abstract

One-dimensional single-chain magnets offer a unique platform for studying the interplay of crystal-field effects, exchange interactions, and lattice dynamics. Here, we investigate spin excitations in Sr4Mn2CoO9 using inelastic neutron scattering (INS) and theoretical modelling. INS reveals two low-energy magnetic excitations at 4 and 7 meV from Mn-Co-Mn spin chains, alongside higher-energy crystal-electric-field (CEF) excitations from two crystallographically inequivalent Co2+ sites. Interestingly, these spin excitations persist at room temperature, demonstrating dynamic magnetic correlations in the absence of long-range order. Furthermore, the crystal-field modelling, based on Stevens operator formalism, reproduces well the CEF spectra, establishing Ising-like Kramers ground-state doublets with strong uniaxial magnetic anisotropy for both Co2+ ions. In addition, the spin wave simulation using SpinW reproduces the spin excitation spectrum and reveals microscopic exchange interactions in two non-interacting Mn-Co-Mn spin chains. Finally, machine-learning lattice-dynamics calculations confirm the phonon spectrum and spin-phonon coupling. By projecting the exchange Hamiltonian onto CEF ground-state doublets, we estimate exchange-induced splittings matching the observed excitations. Thus, our results elucidate low-energy spin dynamics arising from combined crystal-field anisotropy and exchange interactions, with the persistent low-energy excitation providing a microscopic pathway for thermally activated spin relaxation. Furthermore, this work delivers a unified microscopic understanding of the interplay between crystal-field effects, magnetic exchange, and lattice dynamics in Sr4Mn2CoO9, advancing insights into spin dynamics in low-dimensional transition-metal oxides.

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G. Roy, S. Ghosh, M. Kumar, E. Kushwaha, J. Sannigrahi, V. Caignaert, W. Prellier, D. T. Adroja, D. Voneshen, V. Hardy, T. Basu. 2026-08-14. Microscopic investigation of spin dynamics in the single-chain magnet Sr4Mn2CoO9. https://arxiv.org/abs/2608.14222

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