Strain-tunable magnetic correlations in spin liquid candidate Nb$_3$Cl$_8$

Abstract: Recent research suggests the possibility of the two-dimensional breathing-Kagome magnet Nb$_3$Cl$_8$ hosting a quantum spin liquid state, warranting further study into its magnetic properties. Using ab initio calculations, we show that monolayer Nb$_3$Cl$_8$ has short-range antiferromagnetic correlations among Nb$_3$ trimers with S = 1/2, and becomes magnetically frustrated due to the underlying effective triangular lattice geometry, and is evidenced by a frustration index of f > 1. The high-temperature susceptibility shows a negative Weiss temperature from Monte Carlo calculations. Considering spin-orbit coupling, we investigate the magnetic anisotropy, including anisotropic exchange, single-ion anisotropy and the Dzyaloshinskii-Moriya interaction using the four-state energy mapping formalism. Although the elements have relatively small atomic numbers, the Dzyaloshinskii-Moriya interaction is comparable in magnitude to the anisotropic exchange. Additionally, we show that biaxial strain tunes the short-range correlations between antiferromagnetic, paramagnetic and ferromagnetic. These findings strengthen our understanding of Nb$_3$Cl$_8$ and advance its applications in current condensed matter physics and materials science research, including nanoscale mechanical and spintronics applications.