Nb Cl Demonstrates F > 1 Frustration and Potential Quantum Spin Liquid Behaviour

Scientists are increasingly focused on understanding quantum spin liquids, and new research into the two-dimensional material niobium chloride (NbCl) offers compelling insights into this exotic state of matter. Tharindu Fernando and Ting Cao, both from the University of Washington, alongside their colleagues, demonstrate that NbCl exhibits short-range antiferromagnetic correlations and magnetic frustration , key characteristics of a potential quantum spin liquid. Their ab initio calculations reveal how applying biaxial strain can actually tune these magnetic correlations between antiferromagnetic, paramagnetic and ferromagnetic states, a finding which significantly advances our understanding of this material and opens doors for potential applications in nanoscale and spintronics technologies.

Nb3Cl8’s Magnetic Frustration and Anisotropy are remarkably complex

This finding challenges conventional expectations and opens new avenues for exploring complex magnetic phenomena in light-element materials. The team’s calculations accurately model the magnetic properties of Nb3Cl8, providing essential insights for assessing its potential to host exotic quantum states and advance applications in condensed matter physics and materials science. Researchers focused on Nb3Cl8 due to its breathing Kagome lattice, comprised of alternating large and small Nb3 triangles, where each small triangle hosts a shared molecular orbital with a S = 1/2 moment. This unique structure effectively behaves as a triangular lattice magnet, with each trimer representing a vertex, naturally supporting magnetic frustration. The work extends beyond isotropic exchange by incorporating spin-orbit coupling, which introduces anisotropy and extends the role of extended-neighbor interactions, providing a more accurate and comprehensive model of the material’s magnetic landscape. The research establishes a foundation for realizing controllable quantum magnetism and exploring novel quantum states within this intriguing material.

Nb3Cl8 Magnetic Anisotropy via First Principles

The study pioneered a comprehensive approach to understanding magnetic anisotropy in this material, extending beyond previous simplified models to incorporate crucial interactions. Researchers utilised density functional theory (DFT) with U and spin-orbit coupling (SOC) to perform first-principles calculations, providing a robust foundation for subsequent analysis. The team determined these parameters within a unified framework, ensuring internal consistency and accuracy. From the anisotropic exchange, Jk ij, components of the DMI vectors were calculated as Dk x = 1/2(Jk yz −Jk zy), Dk y = 1/2(Jk zx −Jk xz), and Dk z = 1/2(Jk xy −Jk yx).

To further probe the magnetic behaviour, scientists harnessed classical Monte Carlo simulations to calculate the magnetic susceptibility as a function of temperature. Researchers meticulously calculated the anisotropic exchange parameters, finding J1 = 1.49 −0.15 0.89 0.15 1.59 −0.01 −0.89 −0.01 1.47 meV, J2 = 0.96 0.00 0.04 0.00 0.97 −0.02 −0.04 0.02 0.95 meV, and J3 = −0.73 0.00 0.00 0.00 −0.74 0.00 0.00 0.00 −0.73 meV, alongside a single-ion anisotropy constant of A = 0.56 meV. The DMI vector was calculated as D1 = (0, −0.89, −0.15) meV, providing crucial insight into chiral interactions within the system.,.

NbCl monolayer reveals frustrated magnetism and anisotropy at

Data shows that for 0% strain, the diagonal components of J1 are −1.57, −0.34, 0.61, 0.33, −1.47, 0.00, −0.62, 0.00, and −1.57 meV, while for −3% strain, the single-ion anisotropy A reaches 0.46 meV, and J1 becomes −1.57, −0.34, 0.61, 0.33, −1.47, 0.00, −0.62, 0.00, and −1.57 meV. Further analysis at −4% strain reveals a single-ion anisotropy A of 0.43 meV, alongside J1 values of −2.79, −0.38, 0.48, 0.39, −2.69, 0.01, −0.47, 0.01, and −2.79 meV. Measurements confirm that for −3% strain, the angles (θx, θy, θz) are (−0.6 ±0.4, 0.8 ±0.4, −1.2 ±0.4), while for −4% strain, they are (12.6 ±0.4, 12.4 ±0.4, 11.6 ±0.4). These results indicate a transition from near-paramagnetic behaviour at −3% strain to short-range ferromagnetic correlations at −4% strain.

Ab initio supercell calculations, with spin-orbit coupling included, reveal that the unstrained structure favours a 120◦ antiferromagnetic ground state, with an energy of 0.39 meV per unit cell higher than the stripe configuration, and 1.55 meV higher than the ferromagnetic configuration. Notably, at −4% strain, ferromagnetic configurations exhibit the lowest energy, surpassing the 120◦ configurations by approximately 2.05 meV per unit cell, and the stripe configurations by 2.45 meV per unit cell. Spin-spiral calculations corroborate these findings, demonstrating a minimum in the dispersion at the K point for 0% strain, consistent with 120◦ AFM order, and a shift towards the Γ point for −4% strain, suggesting a tendency towards FM order.