# Evolution of Structure and Magnetism in FeCl2 and FeCl3: From Clusters to Monolayers

## TL;DR

This paper studies how the structure and magnetism of iron-chloride clusters change as they grow into monolayers, revealing how magnetic properties evolve.

## Contribution

The study provides new insights into the evolution of magnetic properties from clusters to monolayers in iron-chloride systems.

## Key findings

- FeCl2 and FeCl3 clusters show magnetic properties, while their dimers are antiferromagnetic.
- Li-functionalization can switch antiferromagnetic dimers to ferromagnetic states.
- FeCl2 monolayers are ferromagnetic, while FeCl3 monolayers have nearly degenerate magnetic states.

## Abstract

In this work, we
address one of the most fundamental
questions
in cluster sciencehow do the structure and properties evolve
from clusters to crystals? Using density functional theory (DFT),
we focus our study on the evolution of structure and magnetism in
iron-chloride systems, from clusters to monolayers. The choice of
this system is motivated by the recent experimental confirmation of
one of the author’s earlier theoretical prediction that the
FeCl2 cluster is magnetic with a spin magnetic moment of
4 μB localized at the Fe site, while its dimer, Fe2Cl4, is antiferromagnetic. Similarly, FeCl3 cluster is magnetic with a total spin magnetic moment of
5 μB, with 4 μB localized at the
Fe site and 1 μB distributed over the Cl sites. The
dimer clusters Fe2Cl4 and Fe2Cl6 have an antiferromagnetic ground state, and upon Li-functionalization,
both can be magnetically transformed from antiferromagnetic to ferromagnetic
states. In contrast, FeCl2 and FeCl3 monolayers
exhibit different magnetic ground states in their periodic forms:
FeCl2 is ferromagnetic (FM), but in FeCl3, the
antiferromagnetic (AFM) and FM states are energetically nearly degenerate.
Such a difference arises due to the different chemical coordination
of the Fe atoms with the Cl atoms, caused by their different oxidation
states, which is +2 in FeCl2 and +3 in FeCl3, respectively. Interestingly, Li-functionalization allows both FeCl3 and FeCl2 monolayers to be ferromagnetic. Our
study highlights that several, but not all, electronic and magnetic
characteristics of isolated clusters are preserved in the extended
periodic structures. This systematic investigation of iron-halide
clusters is expected to inspire further experimental and theoretical
exploration into the magnetism of other transition metal halides.