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 η is the only material parameter needed to describe all the experimental evidence. Our experiments suggest a proportionality between η and the strength of the magneto-crystalline anisotropy.
@article{arxiv.2109.03076,
title = {Inertial spin dynamics in epitaxial cobalt films},
author = {Vivek Unikandanunni and Rajasekhar Medapalli and Marco Asa and Edoardo Albisetti and Daniela Petti and Riccardo Bertacco and Eric E. Fullerton and Stefano Bonetti},
journal= {arXiv preprint arXiv:2109.03076},
year = {2022}
}