Micromagnetic study of inertial spin waves in ferromagnetic nanodots

TL;DR

This paper explores the excitation and behavior of ultra-short inertial spin waves in ferromagnetic nanodots using a combination of analytical theory and micromagnetic simulations, highlighting their finite propagation speed and decay characteristics.

Contribution

It introduces a theoretical framework for inertial spin waves and demonstrates their excitation in nanodots through numerical simulations, advancing understanding of ultra-fast magnetic dynamics.

Findings

Inertial spin waves can be excited at terahertz frequencies.

Spin waves of about 20 nm length propagate with finite speed.

Theoretical predictions align with micromagnetic simulation results.

Abstract

Here we report the possibility to excite ultra-short spin waves in ferromagnetic thin-films by using time-harmonic electromagnetic fields with terahertz frequency. Such ultra-fast excitation requires to include inertial effects in the description of magnetization dynamics. In this respect, we consider the inertial Landau-Lifshitz-Gilbert (iLLG) equation and develop analytical theory for exchange-dominated inertial spin waves. The theory predicts a finite limit for inertial spin wave propagation velocity, as well as spin wave spatial decay and lifetime as function of material parameters. Then, guided by the theory, we perform numerical micromagnetic simulations that demonstrate the excitation of ultra-short inertial spin waves (20 nm long) propagating at finite speed in a confined magnetic nanodot. The results are in agreement with the theory and provide the order of magnitude of quantities observable in realistic ultra-fast dynamics experiments.