Orbital-excitation-dominated magnetization dissipation and quantum oscillation of Gilbert damping in Fe films

TL;DR

This study reveals that orbital excitations dominate spin dissipation and Gilbert damping in Fe films, with quantum oscillations observed at low temperatures, enhancing understanding of magnetic damping mechanisms.

Contribution

It introduces a first-principles mechanism showing orbital excitations as the main channel for spin dissipation in Fe, supported by experimental validation.

Findings

Orbital excitations efficiently convert spin to orbital angular momentum.

Gilbert damping in Fe is dominated by orbital excitation mechanisms below room temperature.

Thickness-dependent damping oscillations are observed due to quantum well states.

Abstract

Using first-principles electronic structure calculation, we demonstrate the spin dissipation process in bulk Fe by orbital excitations within the energy bands of pure spin character. The variation of orbitals in the intraband transitions provides an efficient channel to convert spin to orbital angular momentum with spin-orbit interaction. This mechanism dominates the Gilbert damping of Fe below room temperature. The theoretical prediction is confirmed by the ferromagnetic resonance experiment performed on single-crystal Fe(001) films. A significant thickness-dependent damping oscillation is found at low temperature induced by the quantum well states of the corresponding energy bands. Our findings not only explain the microscopic nature of the recently reported ultralow damping of Fe-based alloys, but also help for the understanding of the transport and dissipation process of orbital currents.