Frustration induced one-dimensionality in the isosceles triangular antiferromagnetic lattice of $\delta$-(EDT-TTF-CONMe$_{2}$)$_{2}$AsF$_6$

TL;DR

This study investigates how frustration in a two-dimensional triangular lattice of an organic compound induces one-dimensional magnetic behavior, revealing that structural defects locally relieve frustration and enable antiferromagnetic order.

Contribution

It demonstrates that frustration prevents true magnetic order in defect-free regions, with antiferromagnetic order nucleating around structural defects, highlighting the role of defects in magnetic ordering.

Findings

Frustration inhibits magnetic order down to 4 K in defect-free regions.

Antiferromagnetic order nucleates around structural defects.

Two AFM resonance modes correspond to one-dimensional chains.

Abstract

The $1/4$-filled organic compound, $\delta$-(EDT-TTF-CONMe$_{2}$)$_{2}$AsF$_6$ is a frustrated two-dimensional triangular magnetic system as shown by high-frequency (111.2 and 222.4 GHz) electron spin resonance (ESR) and structural data in the literature. The material gradually orders antiferromagnetically below 40~K but some magnetically disordered domains persist down to 4 K. We propose that in defect free regions frustration prevents true magnetic order down to at least 4 K in spite of the large first- and second-neighbor exchange interactions along chains and between chains, respectively. The antiferromagnetic (AFM) order gradually developing below 40 K nucleates around structural defects that locally cancel frustration. Two antiferromagnetic resonance modes mapped in the principal planes at 4~K are assigned to the very weakly interacting one-dimensional molecular chains in antiferromagnetic regions.