Theoretical determination of Gilbert damping in reduced dimensions

TL;DR

This paper presents a first-principles method to calculate intrinsic Gilbert damping in low-dimensional magnetic systems, revealing substrate effects, adatom position dependence, anisotropy, and magnetic configuration influences on damping.

Contribution

The authors develop an ab initio scheme within the Kubo-Greenwood framework to compute site-dependent Gilbert damping tensors in reduced-dimensional magnets.

Findings

Damping parameters vary with substrate and adatom position.

Anisotropic damping observed when rotating magnetic moments.

Antiferromagnetic dimers exhibit significantly higher damping than ferromagnetic ones.

Abstract

An ab initio scheme based on the Kubo-Greenwood linear response theory of exchange torque correlation is presented to calculate intrinsic Gilbert damping parameters in magnets of reduced dimensions. The method implemented into the real-space Korringa-Kohn-Rostoker (RS-KKR) Greens' function framework enables to obtain diagonal elements of the atomic-site-dependent on-site and non-local Gilbert damping tensor. Going from the 3D bulk and surfaces of iron and cobalt ferromagnets addressed in our previous work [Phys. Rev. B 109, 094417 (2024)], in the present paper monolayers of Fe and Co on (001)- and (111)-oriented Cu, Ag, and Au substrates are studied, and particularly the substrate-dependent trends are compared. Furthermore, the Gilbert damping parameters are calculated for Fe and Co adatoms and dimers on (001)-oriented substrates. It is investigated how the damping parameter of single adatoms depends on their vertical position. This dependence is quantified in relation to the adatoms' density of states at the Fermi energy showing a non-monotonic behavior. By rotating the spin moment of the adatoms and collinear magnetic dimers, an anisotropic behavior of the damping is revealed. Finally, a significant, three- to ten-times increase of the on-site Gilbert damping is found in antiferromagnetic dimers in comparison to the ferromagnetic ones, whilst the inter-site damping is even more enhanced.