First-principles study of magnetic structures of triangular antiferromagnets NaYbS$_2$ and NaYbO$_2$

TL;DR

This study uses first-principles calculations and Monte Carlo simulations to explore the magnetic structures of NaYbO2 and NaYbS2, revealing complex ground states influenced by exchange interactions and aligning with experimental data.

Contribution

It provides a detailed analysis of magnetic interactions in NaYbO2 and NaYbS2, highlighting the importance of second neighbor interactions in determining their ground states.

Findings

NaYbO2's ground state becomes a Z2 vortex phase with second neighbor interactions.

Simulated transition temperatures are higher than experimental observations.

Specific heat simulations match experimental data with no clear phase transition.

Abstract

We investigate the magnetic interactions in triangular rare-earth delafossites materials NaYbO$_2$ and NaYbS$_2$ via first-principles calculations. The calculated Curie-Weiss temperatures are in good agreement with experiments. We perform classical Monte Carlo simulations of the two compounds using the extracted exchange parameters. We find that if only the nearest neighbor interactions are considered, the magnetic ground states of NaYbO$_2$ and NaYbS$_2$ are a stripe and a planar 120\degree~ N\'{e}el state, respectively. The simulated transition temperatures are much higher than the lowest experimental temperatures, where no magnetic ordering was observed. However, we show by adding suitable second neighbor interactions, the {\it classical} magnetic ground state of NaYbO$_2$ becomes to the $Z_2$ vortex phase, and the simulated specific heat $C_v$ are very similar to the experimental observations, with no obvious phase transition down to the extremely low temperature.