$x$-[Pd(dmit)$_2$]$_2$ as a quasi-1D, scalene Heisenberg model

TL;DR

This study uses first-principles calculations to reveal that a family of Pd(dmit)2 compounds exhibits a scalene triangular Heisenberg model with quasi-one-dimensional magnetic behavior and predicts their Néel ordering temperatures.

Contribution

It provides the first atomistic, first-principles analysis of magnetic interactions in these compounds, identifying a scalene triangular model with significant anisotropy and frustration.

Findings

Strong exchange coupling along one axis is up to three times larger than others.

Frustration enhances the quasi-one-dimensionality of the system.

Calculated Néel temperatures agree well with experimental data.

Abstract

From first principles, we calculate the Heisenberg interactions between neighboring dimers in several compounds within the Et$_{n}$Me$_{4-n}X$[Pd(dmit)$_2$]$_2$ (Et = ethyl, Me = methyl, dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate) family using an atomistic approach; with broken-symmetry density functional theory. In all materials, we find a scalene triangular model where the strongest exchange coupling along one crystallographic axis is up to three times larger than the others and that frustration further enhances this quasi-one-dimensionality. We calculate the N\'eel ordering temperature via the chain random phase approximation (CRPA). We show that the difference in the frustrated interchain couplings is equivalent to a single bipartite interchain coupling, favoring long-range magnetic order. We find that the N\'eel ordering temperatures are in good agreement with the experimentally measured values for most compounds.