Giant magnetic anisotropy of Co, Ru, and Os adatoms on MgO (001) surface

TL;DR

This study explains and predicts large magnetic anisotropy energies for Co, Ru, and Os adatoms on MgO (001), highlighting their potential for atomic-scale magnetic memory devices.

Contribution

The paper combines ligand-field theory and density functional calculations to explain and predict giant MAE values for transition metal adatoms on MgO (001).

Findings

Co adatom has MAE > 60 meV.

Predicted MAE up to 110 meV for Ru adatoms.

Os adatoms could have MAE as high as 208 meV.

Abstract

Large magnetic anisotropy energy (MAE) is desirable and critical for nanoscale magnetic devices. Here, using ligand-field level diagrams and density functional calculations, we well explain the very recent discovery [I. G. Rau et al., Science 344, 988 (2014)] that an individual Co adatom on a MgO (001) surface has a large MAE of more than 60 meV. More importantly, we predict that a giant MAE up to 110 meV could be realized for Ru adatoms on MgO (001), and even more for the Os adatoms (208 meV). This is a joint effect of the special ligand field, orbital multiplet, and significant spin-orbit interaction, in the intermediate-spin state of the Ru or Os adatoms on top of the surface oxygens. The giant MAE could provide a route to atomic scale memory.