Comparative study of electronic and magnetic properties of $M$Pc ($M$ = Fe, Co) molecules physisorbed on 2D MoS$_2$ and graphene

TL;DR

This study compares the electronic and magnetic properties of FePc and CoPc molecules physisorbed on monolayer MoS$_2$ and graphene, revealing site preferences, binding energies, and magnetic anisotropy effects through density functional theory.

Contribution

It provides a detailed computational analysis of molecule-surface interactions, highlighting differences in adsorption sites, energies, and magnetic properties on two prominent 2D materials.

Findings

FePc prefers S-top site on MoS$_2$ and bridge/top on graphene.

MoS$_2$ exhibits stronger physisorption than graphene (~2.5 eV higher energy).

Physisorption reduces MoS$_2$ work function by ~1 eV, with minimal effect on magnetic anisotropy.

Abstract

In this paper, we have done a comparative study of electronic and magnetic properties of iron phthalocyanine (FePc) and cobalt phthalocyanine (CoPc) molecules physisorbed on monolayer of MoS$_2$ and graphene by using density functional theory. Various different types of physisorption sites have been considered for both surfaces. Our calculations reveal that the $M$Pc molecules prefer the S-top position on MoS$_2$. However, on graphene, FePc molecule prefers the bridge position while CoPc molecule prefers the top position. The $M$Pc molecules are physisorbed strongly on the MoS$_2$ surface than the graphene ($\sim$ 2.5 eV higher physisorption energy). Analysis of magnetic properties indicates the presence of strong spin dipole moment opposite to the spin moment and hence a huge reduction of effective spin moment can be observed. Our calculations of magnetic anisotropy energies using both variational approach and $2^{nd}$ order perturbation approach indicate no significant changes after physisorption. In case of FePc, an out-of-plane easy axis and in case of CoPc, an in-plane easy axis can be seen. Calculations of work function indicate a reduction of MoS$_2$ work function $\sim$ 1 eV due to physisorption of $M$Pc molecules while it does not change significantly in case of graphene.