Evaluating the locality of intrinsic precession damping in transition metals

TL;DR

This study investigates whether the damping of magnetic precession in transition metals is local or non-local, finding that at typical temperatures damping is mostly local, but non-local effects become significant at cryogenic temperatures in pure samples.

Contribution

It provides the first detailed calculation of non-local effects on intrinsic damping in transition metals, challenging the assumption of purely local damping in practical conditions.

Findings

Damping rates are largely unaffected by magnon wavelength at room temperature.

Non-local effects significantly reduce damping at cryogenic temperatures in pure samples.

Damping shows little dependence on magnon propagation direction.

Abstract

The Landau-Lifshitz-Gilbert damping parameter is typically assumed to be a local quantity, independent of magnetic configuration. To test the validity of this assumption we calculate the precession damping rate of small amplitude non-uniform mode magnons in iron, cobalt, and nickel. At scattering rates expected near and above room temperature, little change in the damping rate is found as the magnon wavelength is decreased from infinity to a length shorter than features probed in recent experiments. This result indicates that non-local effects due to the presence of weakly non-uniform modes, expected in real devices, should not appreciably affect the dynamic response of the element at typical operating temperatures. Conversely, at scattering rates expected in very pure samples around cryogenic temperatures, non-local effects result in an order of magnitude decrease in damping rates for magnons with wavelengths commensurate with domain wall widths. While this low temperature result is likely of little practical importance, it provides an experimentally testable prediction of the non-local contribution of the spin-orbit torque-correlation model of precession damping. None of these results exhibit strong dependence on the magnon propagation direction.