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<p>Motivated by the on-going discussion on the nature of magnetism in the quantum Ising chain CoNb<sub>2</sub>O<sub>6</sub>, we present a first-principles-based analysis of its exchange interactions with additional modeling, addressing drawbacks of a purely density functional theory ansatz. This method allows us to extract and understand the origin of the magnetic couplings—including all symmetry-allowed terms - and resolve conflicting model descriptions in CoNb<sub>2</sub>O<sub>6</sub>. We find that the twisted Kitaev chain and transverse-field ferromagnetic Ising chain views are mutually compatible, although additional off-diagonal exchanges are required for a complete picture. We show that the dominant exchange interaction is a ligand-centered process—involving <i>e</i><sub><i>g</i></sub> electrons -, rendered anisotropic by low-symmetry crystal fields in CoNb<sub>2</sub>O<sub>6</sub>, resulting in dominant Ising exchange. Smaller bond-dependent anisotropies are found to originate from <i>d</i> − <i>d</i> kinetic exchange processes involving <i>t</i><sub>2<i>g</i></sub> electrons. We demonstrate the validity of our low-energy model by comparing its predictions to measured THz and INS spectra.</p>

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Understanding the microscopic origin of the magnetic interactions in CoNb2O6

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  • 发表日期：

    2025年1月18日

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  • Amanda A. Konieczna,
  • David A. S. Kaib,
  • Stephen M. Winter,
  • Roser Valentí

摘要

Motivated by the on-going discussion on the nature of magnetism in the quantum Ising chain CoNb2O6, we present a first-principles-based analysis of its exchange interactions with additional modeling, addressing drawbacks of a purely density functional theory ansatz. This method allows us to extract and understand the origin of the magnetic couplings—including all symmetry-allowed terms - and resolve conflicting model descriptions in CoNb2O6. We find that the twisted Kitaev chain and transverse-field ferromagnetic Ising chain views are mutually compatible, although additional off-diagonal exchanges are required for a complete picture. We show that the dominant exchange interaction is a ligand-centered process—involving eg electrons -, rendered anisotropic by low-symmetry crystal fields in CoNb2O6, resulting in dominant Ising exchange. Smaller bond-dependent anisotropies are found to originate from d − d kinetic exchange processes involving t2g electrons. We demonstrate the validity of our low-energy model by comparing its predictions to measured THz and INS spectra.