Inertial spin dynamics in epitaxial cobalt films

TL;DR

This study explores how terahertz magnetic fields induce ultrafast spin precession in epitaxial cobalt films, revealing the role of magnetic inertia and anisotropy in spin dynamics.

Contribution

It demonstrates the application of the inertial Landau-Lifshitz-Gilbert equation to describe spin precession in cobalt films, linking magnetic inertia to material properties.

Findings

Magnetization precesses for about 1 ps under terahertz excitation.

The angular momentum relaxation time $ta$ correlates with magneto-crystalline anisotropy.

Experimental data aligns with the relativistic theory of magnetic inertia.

Abstract

We investigate the spin dynamics driven by terahertz magnetic fields in epitaxial thin films of cobalt in its three crystalline phases. The terahertz magnetic field generates a torque on the magnetization which causes it to precess for about 1 ps, with a sub-picosecond temporal lag from the driving force. Then, the magnetization undergoes natural damped THz oscillations at a frequency characteristic of the crystalline phase. We describe the experimental observations solving the inertial Landau-Lifshitz-Gilbert equation. Using the results from the relativistic theory of magnetic inertia, we find that the angular momentum relaxation time $\eta$ is the only material parameter needed to describe all the experimental evidence. Our experiments suggest a proportionality between $\eta$ and the strength of the magneto-crystalline anisotropy.