Intrinsic energy flow in laser-excited 3$d$ ferromagnets

TL;DR

This study combines experiments and simulations to understand the ultrafast energy flow among electronic, magnetic, and lattice systems in 3d ferromagnets, revealing the dominant role of the spin system in initial femtoseconds.

Contribution

It introduces an integrated approach using femtosecond electron diffraction, atomistic spin dynamics, and ab-initio calculations to accurately model energy flow in Co and Fe.

Findings

Lattice dynamics are significantly affected by magnetization dynamics.

Spin system acts as the main heat sink in the first hundreds of femtoseconds.

Energy-conserving ASD simulations accurately describe laser-induced dynamics in 3d ferromagnets.

Abstract

Ultrafast magnetization dynamics are governed by energy flow between electronic, magnetic, and lattice degrees of freedom. A quantitative understanding of these dynamics must be based on a model that agrees with experimental results for all three subsystems. However, ultrafast dynamics of the lattice remain largely unexplored experimentally. Here, we combine femtosecond electron diffraction experiments of the lattice dynamics with energy-conserving atomistic spin dynamics (ASD) simulations and ab-initio calculations to study the intrinsic energy flow in the 3d ferromagnets cobalt (Co) and iron (Fe). The simulations yield a good description of experimental data, in particular an excellent description of our experimental results for the lattice dynamics. We find that the lattice dynamics are influenced significantly by the magnetization dynamics due to the energy cost of demagnetization. Our results highlight the role of the spin system as the dominant heat sink in the first hundreds of femtoseconds. Together with previous findings for nickel [Zahn et al., Phys. Rev. Research 3, 023032 (2021)], our work demonstrates that energy-conserving ASD simulations provide a general and consistent description of the laser-induced dynamics in all three elemental 3d ferromagnets.