Strong spin-orbit induced Gilbert damping and g-shift in iron-platinum nanoparticles

TL;DR

This study investigates the enhanced Gilbert damping and g-shift in FePt nanoparticles, attributing these effects to spin-orbit coupling-mediated electron-hole pair scattering, with implications for magnetic damping mechanisms.

Contribution

It demonstrates that spin-orbit coupling causes significant damping and g-shift in FePt nanoparticles, highlighting a new scattering mechanism involving electron-hole pairs.

Findings

Damping parameter α(0)=0.76 at zero temperature

Negative g-shift g(0)/g_0-1=-0.37 at zero temperature

Damping and g-shift increase with temperature, proportional to magnetic moments

Abstract

The shape of ferromagnetic resonance spectra of highly dispersed, chemically disordered Fe_{0.2}Pt_{0.8} nanospheres is perfectly described by the solution of the Landau-Lifshitz-Gilbert (LLG) equation excluding effects by crystalline anisotropy and superparamagnetic fluctuations. Upon decreasing temperature, the LLG damping $\alpha(T)$ and a negative g-shift, g(T)-g_0, increase proportional to the particle magnetic moments determined from the Langevin analysis of the magnetization isotherms. These novel features are explained by the scattering of the $q \to 0$ magnon from an electron-hole (e/h) pair mediated by the spin-orbit coupling, while the sd-exchange can be ruled out. The large saturation values, $\alpha(0)=0.76$ and $g(0)/g_0-1=-0.37$, indicate the dominance of an overdamped 1 meV e/h-pair which seems to originate from the discrete levels of the itinerant electrons in the d_p=3 nm nanoparticles.