We use single-cycle THz fields and the femtosecond magneto-optical Kerr effect to respectively excite and probe the magnetization dynamics in two thin-film ferromagnets with different lattice structure: crystalline Fe and amorphous CoFeB. We observe Landau-Lifshitz-torque magnetization dynamics of comparable magnitude in both systems, but only the amorphous sample shows ultrafast demagnetization caused by the spin-lattice depolarization of the THz-induced ultrafast spin current. Quantitative modelling shows that such spin-lattice scattering events occur on similar time scales than the conventional spin conserving electronic scattering (∼30 fs). This is significantly faster that optical laser-induced demagnetization. THz conductivity measurements point towards the influence of lattice disorder in amorphous CoFeB as the driving force for enhanced spin-lattice scattering.
@article{arxiv.1604.04077,
title = {THz-driven ultrafast spin-lattice scattering in amorphous metallic ferromagnets},
author = {S. Bonetti and M. C. Hoffmann and M. -J. Sher and Z. Chen and S. -H. Yang and M. Samant and S. S. P. Parkin and H. A. Dürr},
journal= {arXiv preprint arXiv:1604.04077},
year = {2016}
}