Magnetocrystalline anisotropy energy for adatoms and monolayers on non-magnetic substrates: where does it comes from?

TL;DR

This study systematically analyzes the substrate's role in magnetic anisotropy energy of Co adatoms and monolayers on various non-magnetic metal surfaces, highlighting the dominant influence of spin-orbit coupling and substrate effects on magnetic orientation.

Contribution

It provides a detailed, site-selective investigation of substrate contributions to MAE, emphasizing the importance of SOC over exchange fields and the impact of substrate polarizability.

Findings

Substrate contribution to MAE is small for adatoms but significant for monolayers.

SOC effects dominate over exchange field contributions in determining MAE.

Substrates generally favor out-of-plane magnetic easy axes.

Abstract

The substrate contribution to the magnetic anisotropy energy (MAE) of supported nanostructures can be quantified by a site-selective manipulation of the spin-orbit coupling (SOC) and the effective exchange field B_ex. A systematic study of Co adatoms and Co monolayers on the (111) surfaces of Cu, Ag, Au, Pd and Pt is performed to study common trends in this class of materials. It is found that for adatoms, the substrate contribution is relatively small (10-30% of the MAE) while for monolayers, the substrate contribution can be substantial. The contribution from the SOC is much more important than the contribution from the exchange field B_ex, except for highly polarizable substrates with a strong SOC (such as Pt). The substrate always promotes the tendency to an out-of-plane orientation of the easy magnetic axis for all the investigated systems.