In this paper, we have done a comparative theoretical study of electronic and magnetic properties of iron phthalocyanine (FePc) and cobalt phthalocyanine (CoPc) molecules physisorbed on a monolayer of ${\mathrm{MoS}}_2$ and graphene by density functional theory. Various types of physisorption sites have been considered for both surfaces. The lowest energy structure for both metal phthalocyanine ($M\mathrm{Pc}$) molecules physisorbed on ${\mathrm{MoS}}_2$ is a sulfur-top position, i.e., when the metal center of the molecule is on top of a sulfur atom. However, on graphene, the lowest energy structure for the FePc molecule is when a metal atom is on top of a bridge position. In contrast to this, the CoPc molecule prefers a carbon-top position. The adsorption of $M\mathrm{Pc}$ molecules is stronger on the ${\mathrm{MoS}}_2$ surface than on graphene ($\sim 2.5$ eV higher physisorption energy). In these systems, spin dipole moments of the metal centers are antiparallel to the spin moments and hence a huge reduction of effective spin moment can be seen. The calculations of magnetic anisotropy energies using both variational and second-order perturbation approaches indicate no significant changes after physisorption. In case of the FePc and CoPc physisorption, respectively, an out-of-plane and an in-plane easy axis of magnetization can be observed. Our calculations indicate a reduction of ${\mathrm{MoS}}_2$ work function $\sim 1$ eV due to physisorption of $M\mathrm{Pc}$ molecules while it does not change significantly in the case of graphene.

• Received 21 March 2018
• Revised 6 July 2018

DOI:https://doi.org/10.1103/PhysRevB.98.085440