Anisotropic magnetoelastic coupling in the honeycomb magnet Na$_3$Co$_2$SbO$_6$

TL;DR

This study investigates the anisotropic magnetoelastic effects and phase transitions in the honeycomb magnet Na$_3$Co$_2$SbO$_6$, revealing complex magnetic behavior without evidence of a quantum spin liquid state.

Contribution

It provides detailed magnetization and dilatometry data, mapping the phase diagram and elucidating the anisotropic magnetoelastic coupling and nature of magnetic transitions in Na$_3$Co$_2$SbO$_6$.

Findings

Strong anisotropic lattice response to in-plane magnetic fields.

Step-like features in magnetization indicating complex magnetic transitions.

Absence of quantum critical behavior or quantum spin liquid state near critical fields.

Abstract

We present magnetization and dilatometry measurements on the honeycomb cobaltate Na$_3$Co$_2$SbO$_6$ and map out its detailed field-temperature phase diagram down to sub-Kelvin temperatures. Our data for in-plane magnetic fields show a strongly anisotropic $c^{*}$-axis lattice response, which is dominated by the variation of Co--O--Co bond angles according to \textit{ab initio} calculations. At $T = 0.4$~K, the magnetization $M(B)$ exhibits step-like features that are also highly anisotropic. In the case of $B \parallel b$, a small hysteresis observed around the second field-induced magnetic transition ($B_{c2}$) indicates its first-order character, whereas divergence of the magnetic Gr\"uneisen parameter at $B_{c2}$ is suppressed upon cooling and signals the absence of quantum critical behavior upon entering the field-polarized state. None of our thermodynamic measurements provide evidence for a field-induced quantum spin liquid state near or above $B_{c2}$.