Magnetic Properties of Metal⁻Organic Coordination Networks Based on 3d Transition Metal Atoms

• Published in: Molecules (Basel, Switzerland) Vol. 23; no. 4; p. 964
• Main Authors: Blanco-Rey, María, Sarasola, Ane, Nistor, Corneliu, Persichetti, Luca, Stamm, Christian, Piamonteze, Cinthia, Gambardella, Pietro, Stepanow, Sebastian, Otrokov, Mikhail M, Golovach, Vitaly N, Arnau, Andres
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 20.04.2018; MDPI
• Subjects: Algorithms; Anisotropy; Antiferromagnetism; Circular dichroism; Crystallography, X-Ray; Density functional theory; Dichroism; Ferromagnetism; Gold; Magnetic anisotropy; Magnetic Phenomena; Magnetic properties; Magnetics - methods; magnetism; Magnetization; Manganese; Metals; Metals - chemistry; metal–organic network; Models, Chemical; Models, Molecular; Spectrum Analysis; Spin-orbit interactions; Stoichiometry; Tetracyanoquinodimethane; Transportation networks; X-ray magnetic circular dichroism (XMCD); magnetism; metal–organic network; X-ray magnetic circular dichroism (XMCD); density functional theory
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules23040964

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 a Au(111) metal surface are studied. In particular, we consider MOCNs made of Ni or Mn metal centers linked by 7,7,8,8-tetracyanoquinodimethane (TCNQ) 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-plane magnetization. We explain these observations using both a model Hamiltonian based on mean-field Weiss 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 by 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.