Inertial terms to magnetization dynamics in ferromagnetic thin films

TL;DR

This paper experimentally identifies inertial terms in the magnetization dynamics of ferromagnetic thin films at high frequencies, revealing a quadratic frequency-dependent stiffening effect near room temperature.

Contribution

It provides the first experimental evidence of inertial effects in ferromagnetic thin films at near-room temperatures, extending the understanding of ultrafast magnetization dynamics.

Findings

Inertial terms cause a quadratic frequency stiffening in magnetization dynamics.

Measured additional magnetic field of approximately 80 mT at high frequencies.

Results extend the understanding of sub-picosecond magnetization processes.

Abstract

Inertial magnetization dynamics have been predicted at ultrahigh speeds, or frequencies approaching the energy relaxation scale of electrons, in ferromagnetic metals. Here we identify inertial terms to magnetization dynamics in thin Ni$_{79}$Fe$_{21}$ and Co films near room temperature. Effective magnetic fields measured in high-frequency ferromagnetic resonance (115-345 GHz) show an additional stiffening term which is quadratic in frequency and $\sim$ 80 mT at the high frequency limit of our experiment. Our results extend understanding of magnetization dynamics at sub-picosecond time scales.