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

摘要

Based on first-principles density functional theory calculations we exploreelectronic and magnetic properties of experimentally producible sandwiches andinfinite wires made of repeating benzene molecules and transition-metal atomsof V, Nb, and Ta. We describe the bonding mechanism in the molecules and inparticular concentrate on the origin of magnetism in these structures. We findthat all the considered systems have sizable magnetic moments and ferromagneticspin-ordering, with the single exception of the V3-Bz4 molecule. By includingthe spin-orbit coupling into our calculations we determine the easy and hardaxes of the magnetic moment, the strength of the uniaxial magnetic anisotropyenergy (MAE), relevant for the thermal stability of magnetic orientation, andthe change of the electronic structure with respect to the direction of themagnetic moment, important for spin-transport properties. While for the V-basedcompounds the values of the MAE are only of the order of 0.05-0.5 meV per metalatom, increasing the spin-orbit strength by substituting V with heavier Nb andTa allows to achieve an increase in anisotropy values by one to two orders ofmagnitude. The rigid stability of magnetism in these compounds together withthe strong ferromagnetic ordering makes them attractive candidates forspin-polarized transport applications. For a Nb-benzene infinite wire theoccurrence of ballistic anisotropic magnetoresistance is demonstrated.