Magnetic properties of metal-organic coordination networks based on 3d transition metal atoms

TL;DR

This study investigates the magnetic properties of 2D metal-organic coordination networks with 3d transition metals, revealing ferromagnetic coupling in Ni-based networks and antiferromagnetic coupling with weak anisotropy in Mn-based networks, using experimental and theoretical methods.

Contribution

It provides new insights into the magnetic interactions and anisotropy in Ni- and Mn-based metal-organic networks on gold surfaces, combining experimental XMCD data with theoretical modeling.

Findings

Ni atoms are ferromagnetically coupled with no significant anisotropy.

Mn atoms are antiferromagnetically coupled with weak in-plane anisotropy.

The surface effects influence the magnetic behavior of Ni-TCNQ networks.

Abstract

The magnetic anisotropy and exchange coupling between spins localized at the positions of 3d transition metal atoms forming two-dimensional metal-organic coordination networks (MOCNs) grown on the Au(111) metal surface are studied. In particular, we consider MOCNs made of Ni or Mn metal centers linked by TCNQ (7,7,8,8-tetracyanoquinodimethane) organic ligands, which form rectangular networks with 1:1 stoichiometry. Based on the analysis of X-ray magnetic circular dichroism (XMCD) data taken at T= 2.5 K, we find that Ni atoms in the Ni-TCNQ MOCNs are coupled ferromagnetically and do not show any significant magnetic anisotropy, while Mn atoms in the Mn-TCNQ MOCNs are coupled antiferromagnetically and do show a weak magnetic anisotropy with in-planemagnetization. We explain these observations using both amodelHamiltonian based on mean-fieldWeiss theory and density functional theory calculations that include spin-orbit coupling. Our main conclusion is that the antiferromagnetic coupling between Mn spins and the in-plane magnetization of the Mn spins can be explained neglecting effects due to the presence of the Au(111) surface, while for Ni-TCNQ the metal surface plays a role in determining the absence of magnetic anisotropy in the system.