Interplay of structure and spin-orbit strength in magnetism of metal-benzene sandwiches: from single molecules to infinite wires

TL;DR

This study uses first-principles calculations to analyze the electronic and magnetic properties of metal-benzene sandwiches and wires, revealing how spin-orbit coupling influences magnetic anisotropy and transport properties, with implications for spintronic applications.

Contribution

It provides a detailed analysis of the magnetic anisotropy and electronic structure in metal-benzene systems, highlighting the impact of spin-orbit coupling and metal choice on magnetic stability and transport.

Findings

All systems exhibit sizable magnetic moments and ferromagnetic order except V3-Bz4.

Increasing spin-orbit strength enhances magnetic anisotropy significantly.

Nb-benzene wire shows ballistic anisotropic magnetoresistance.

Abstract

Based on first-principles density functional theory calculations we explore electronic and magnetic properties of experimentally producible sandwiches and infinite wires made of repeating benzene molecules and transition-metal atoms of V, Nb, and Ta. We describe the bonding mechanism in the molecules and in particular concentrate on the origin of magnetism in these structures. We find that all the considered systems have sizable magnetic moments and ferromagnetic spin-ordering, with the single exception of the V3-Bz4 molecule. By including the spin-orbit coupling into our calculations we determine the easy and hard axes of the magnetic moment, the strength of the uniaxial magnetic anisotropy energy (MAE), relevant for the thermal stability of magnetic orientation, and the change of the electronic structure with respect to the direction of the magnetic moment, important for spin-transport properties. While for the V-based compounds the values of the MAE are only of the order of 0.05-0.5 meV per metal atom, increasing the spin-orbit strength by substituting V with heavier Nb and Ta allows to achieve an increase in anisotropy values by one to two orders of magnitude. The rigid stability of magnetism in these compounds together with the strong ferromagnetic ordering makes them attractive candidates for spin-polarized transport applications. For a Nb-benzene infinite wire the occurrence of ballistic anisotropic magnetoresistance is demonstrated.