Exploring dynamical magnetism with time-dependent density-functional theory: from spin fluctuations to Gilbert damping

TL;DR

This paper employs time-dependent density-functional theory to analyze dynamical magnetic phenomena, introduces a new gradient-dependent functional to improve magnetic fluctuation modeling, and derives the Gilbert equation from first principles.

Contribution

It constructs a new gradient-dependent density functional that overcomes LSDA limitations and derives the Gilbert damping equation directly from density-functional theory.

Findings

The new functional better captures magnetic fluctuations in itinerant ferromagnets.

The Gilbert equation is derived from first principles within this framework.

Comparisons with experiments validate the theoretical approach.

Abstract

We use time-dependent spin-density-functional theory to study dynamical magnetic phenomena. First, we recall that the local-spin-density approximation (LSDA) fails to account correctly for magnetic fluctuations in the paramagnetic state of iron and other itinerant ferromagnets. Next, we construct a gradient-dependent density functional that does not suffer from this problem of the LSDA. This functional is then used to derive, for the first time, the phenomenological Gilbert equation of micromagnetics directly from time-dependent density-functional theory. Limitations and extensions of Gilbert damping are discussed on this basis, and some comparisons with phenomenological theories and experiments are made.