单链磁体Sr4Mn2CoO9中自旋动力学的微观研究
Microscopic investigation of spin dynamics in the single-chain magnet Sr4Mn2CoO9
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中文总结 AI 辅助
本文通过非弹性中子散射、理论建模等方法，研究单链磁体Sr4Mn2CoO9的自旋动力学，揭示其低能自旋激发的微观机制，深化了对低维过渡金属氧化物自旋动力学的理解。
中文摘要 AI 辅助
一维单链磁体为研究晶体场效应、交换相互作用与晶格动力学的相互作用提供了独特平台。本文利用非弹性中子散射（INS）和理论建模研究Sr4Mn2CoO9中的自旋激发。INS从Mn-Co-Mn自旋链中揭示出4 meV和7 meV处的两个低能磁激发，以及来自两个结晶学不等价Co2+位点的更高能晶体电场（CEF）激发。有趣的是，这些自旋激发在室温下依然存在，表明在无长程有序时存在动态磁关联。此外，基于史蒂文斯算符形式的晶体场建模很好地再现了CEF光谱，为两个Co2+离子建立了具有强单轴磁各向异性的类伊辛克拉默斯基态二重态。另外，使用SpinW的自旋波模拟再现了自旋激发光谱，并揭示了两个非相互作用Mn-Co-Mn自旋链中的微观交换相互作用。最后，机器学习晶格动力学计算确认了声子光谱和声子-自旋耦合。通过将交换哈密顿量投影到CEF基态二重态，我们估算了与观测激发匹配的交换诱导分裂。因此，本研究结果阐明了由晶体场各向异性与交换相互作用共同产生的低能自旋动力学，且持续存在的低能激发为热激活自旋弛豫提供了微观途径。此外，本工作实现了对Sr4Mn2CoO9中晶体场效应、磁交换与晶格动力学之间相互作用的统一微观理解，推进了对低维过渡金属氧化物中自旋动力学的认识。
英文摘要
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.
