Interplay between Orbital Magnetic Moment and Crystal Field Symmetry: Fe atoms on MgO

TL;DR

This study investigates how the crystal field symmetry affects the orbital magnetic moment of Fe atoms on MgO, revealing that cubic ligand fields quench the orbital moment despite strong axial fields, with spin-orbit interaction restoring part of it.

Contribution

It provides a detailed analysis of the interplay between orbital magnetic moments and crystal field symmetry for Fe atoms on MgO, highlighting the contrasting behavior with Co atoms.

Findings

Cubic ligand field quenches Fe orbital moment despite axial field.

Spin-orbit interaction restores a significant orbital moment in Fe.

Largest zero-field splitting reported for surface adsorbed Fe atoms.

Abstract

We combine density functional theory, x-ray magnetic circular dichroism, multiplet calculations, and scanning tunneling spectroscopy to assess the magnetic properties of Fe atoms adsorbed on a thin layer of MgO(100) on Ag(100). Despite the strong axial field due to the O ligand, the weak cubic field induced by the four-fold coordination to Mg atoms entirely quenches the first order orbital moment. This is in marked contrast to Co, which has an out-of-plane orbital moment of $L_z = \pm 3$ that is protected from mixing in a cubic ligand field. The spin-orbit interaction restores a large fraction of the Fe orbital moment leading a zero-field splitting of $14.0 \pm 0.3$~meV, the largest value reported for surface adsorbed Fe atoms.