Transition metal dimers as potential molecular magnets: A challenge to computational chemistry

Abstract

Dimers are the smallest chemical objects that show magnetic anisotropy. We focus on 3d and 4d transition metal dimers that have magnetic ground states in most cases. Some of these magnetic dimers have a considerable barrier against re-orientation of their magnetization, the so-called magnetic anisotropy energy, MAE. The height of this barrier is important for technological applications, as it determines, e.g., the stability of information stored in magnetic memory devices. It can be estimated by means of relativistic density functional calculations. Our approach is based on a full-potential local-orbital method (FPLO) in a four-component Dirac-Kohn-Sham implementation. Orbital polarization corrections to the local density approximation are employed. They are discussed in the broader context of orbital dependent density functionals. Ground state properties (spin multiplicity, bond length, harmonic vibrational frequency, spin- and orbital magnetic moment, and MAE) of the 3d and 4d transition metal dimers are evaluated and compared with available experimental and theoretical data. We find exceptionally high values of MAE, close to 0.2 eV, for four particular dimers: Fe(2), Co(2), Ni(2), and Rh(2).

Correlation effects and orbital magnetism of Co clusters

“…This shows that it is possible to stabilize different stable and meta-stable configurations, and may explain the different results of Refs. [18,19]. The small discrepancies between our values for the magnetic moments and the values of Refs.…”

“…[18], while in Ref. [19] the values of orbital and spin moments were respectively 1 µ B /atom and 2.05 µ B /atom. By using different starting densities for our self-consistent calculations, we managed to obtain a state with an orbital moment of 0.34 µ B /atom and a spin moment of 2.08 µ B /atom (see GGA result in Table II) and another state with an orbital moment of 0.94 µ B /atom and a spin moment of 2.11 µ B /atom.…”

“…Namely, this calculation can be compared with the work of Refs. [18,19]. For the ground state of Co 2 , a theoretical orbital moment of 0.39 µ B /atom and a spin moment of 1.95 µ B /atom were reported in Ref.…”

Electronic ground states of Fe2+ and Co2+ as determined by x-ray absorption and x-ray magnetic circular dichroism spectroscopy

“…[13][14][15][16][17][18][19][20][21][22][23] Experimental data, on the other hand, has resisted to yield a conclusive picture. [5][6][7][8][9][10][11][12] From a different point of view, the possibility of aligning molecules in magnetic fields 24,25 and the question of the fundamental limits of the magnetic anisotropy energy that is responsible for a preferred axis of alignment of the magnetic moment naturally lead to diatomic molecules of 3d transition elements and their complexes.…”

“…[5][6][7][8][9][10][11][12] From a different point of view, the possibility of aligning molecules in magnetic fields 24,25 and the question of the fundamental limits of the magnetic anisotropy energy that is responsible for a preferred axis of alignment of the magnetic moment naturally lead to diatomic molecules of 3d transition elements and their complexes. [17][18][19][20] Again, the predicted magnetic anisotropy energy relies on an accurate determination of the electronic states and their relative energies.…”