Understanding the microscopic origin of the magnetic interactions in CoNb\(_2\)O\(_6\)

• Published in: arXiv.org 2024-06
• Main Authors: Konieczna, Amanda A, Kaib, David A S, Winter, Stephen M, Valentí, Roser
• Format: Article
• Language: English
• Subjects: Couplings; Density functional theory; Electrons; Exchanging; Ferromagnetism; First principles; Inelastic scattering; Ising model; Neutron scattering; Neutrons; Symmetry
• ISSN: 2331-8422

Motivated by the on-going discussion on the nature of magnetism in the quantum Ising chain CoNb\(_2\)O\(_6\), we present a first-principles-based analysis of its exchange interactions by applying an \textit{ab initio} approach with additional modelling that accounts for various drawbacks of a purely density functional theory ansatz. With this method we are able to extract and understand the origin of the magnetic couplings under inclusion of all symmetry-allowed terms, and to resolve the conflicting model descriptions in CoNb\(_2\)O\(_6\). We find that the twisted Kitaev chain and the transverse-field ferromagnetic Ising chain views are mutually compatible, although additional off-diagonal exchanges are necessary to provide a complete picture. We show that the dominant exchange interaction is a ligand-centered exchange process - involving the \(e_g\) electrons -, which is rendered anisotropic by the low-symmetry crystal fields environments in CoNb\(_2\)O\(_6\), giving rise to the dominant Ising exchange, while the smaller bond-dependent anisotropies are found to originate from \(d-d\) kinetic exchange processes involving the \(t_{2g}\) electrons. We demonstrate the validity of our approach by comparing the predictions of the obtained low-energy model to measured THz and inelastic neutron scattering spectra.