Magnetism of a Co monolayer on Pt(111) capped by overlayers of $5d$ elements: a spin-model study

TL;DR

This study uses first-principles calculations to analyze how different $5d$ element overlayers affect the magnetic properties of a Co monolayer on Pt(111), revealing changes in exchange interactions, anisotropies, and magnetic ground states.

Contribution

It provides a detailed first-principles analysis of the impact of various $5d$ overlayers on the magnetic interactions and ground states of Co/Pt(111) systems, highlighting the role of spin-orbit coupling and hybridization.

Findings

Dzyaloshinskii-Moriya interaction decreases with overlayers

Ir overlayer causes sign change in Dzyaloshinskii-Moriya interaction

Re/Co/Pt(111) exhibits a spin spiral ground state

Abstract

Using first-principles calculations, we study the magnetic properties of a Co monolayer on a Pt(111) surface with a capping monolayer of selected $5d$ elements (Re, Os, Ir, Pt and Au). First we determine the tensorial exchange interactions and magnetic anisotropies characterizing the Co monolayer for all considered systems. We find a close relationship between the magnetic moment of the Co atoms and the nearest-neighbor isotropic exchange interaction, which is attributed to the electronic hybridization between the Co and the capping layers, in spirit of the Stoner picture of ferromagnetism. The Dzyaloshinskii-Moriya interaction is decreased for all overlayers compared to the uncapped Co/Pt(111) system, while even the sign of the Dzyaloshinskii-Moriya interaction changes in case of the Ir overlayer. We conclude that the variation of the Dzyaloshinskii-Moriya interaction is well correlated with the change of the magnetic anisotropy energy and of the orbital moment anisotropy. The unique influence of the Ir overlayer on the Dzyaloshinskii-Moriya interaction is traced by scaling the strength of the spin--orbit coupling of the Ir atoms in Ir/Co/Pt(111) and by changing the Ir concentration in the Au$_{1-x}$Ir$_{x}$/Co/Pt(111) system. Our spin dynamics simulations indicate that the magnetic ground state of Re/Co/Pt(111) thin film is a spin spiral with a tilted normal vector, while the other systems are ferromagnetic.