Gilbert Damping Parameters of Epitaxially-Stabilized Iron Gallium Thin Films from Ferromagnetic Resonance

TL;DR

This study investigates the magnetic resonance properties of epitaxially-stabilized iron gallium thin films, revealing how increased gallium content reduces damping and enhances magnetoelastic coupling, which is crucial for energy-efficient magnetoelectric devices.

Contribution

It provides the first detailed analysis of ferromagnetic resonance and damping parameters in high-Ga-content epitaxial FeGa films, highlighting the relationship between gallium concentration and magnetic relaxation mechanisms.

Findings

Gilbert damping parameter decreases with higher Ga content.

Magnetoelastic coupling increases as Ga concentration rises.

Effective damping involves magnon-phonon scattering and other mechanisms.

Abstract

Iron gallium (FeGa) alloys are excellent rare-earth-free magnetostrictors. Through epitaxial stabilization, the disordered A2 alloy can be extended from 19% to 30% gallium resulting in a magnetostrictive coefficient almost twice than that which is seen in rare earth magnetostrictors like SmFe2. In a composite magnetoelectric structure, this makes epitaxially-stabilized iron gallium a key material for energy-efficient beyond CMOS technologies. The energy dissipation and speed of magnetoelectric switching, however, is affected by the magnetic resonance frequency and damping. Here we report the evolution of the ferromagnetic resonance and key materials parameters (magnetic anisotropy, magnetic damping, and magnetostriction coefficient) for 70 nm thick epitaxially-stabilized single crystal A2 FeGa films beyond 19% Ga. Using flip chip ferromagnetic resonance (1-14 GHz), we find that the Gilbert damping parameter spans the range of 0.09-0.16 and decreases as the Ga concentration increases. This correlates an increasing magnetoelastic coupling with a reduction in the Gilbert damping. We find that the effective damping is a mix of contributions from the intrinsic magnon-phonon scattering and other scattering/dissipation mechanisms, with the latter being dominant especially at high Ga composition. Our results provide insight into the mechanism of magnetic relaxation in metastable high magnetostriction materials and potential switching behavior of composite magnetoelectrics.