Effect of iron thicknesses on spin transport in a Fe/Au bilayer system

TL;DR

This study uses Monte-Carlo simulations to analyze how varying iron layer thicknesses influence spin current behavior in Fe/Au bilayers excited by femtosecond optical pulses, revealing optimal thickness ranges for spin injection.

Contribution

It provides a detailed theoretical analysis of the impact of layer thicknesses on spin transport in Fe/Au bilayers under high-energy optical excitation, highlighting the role of absorption profiles and interface effects.

Findings

Spin current density is affected by light absorption profiles.

Optimal iron thicknesses enhance spin injection efficiency.

Interface effects are minimal at high electron energies.

Abstract

This paper is concerned with a theoretical analysis of the behavior of optically excited spin currents in bilayer and multilayer systems of ferromagnetic and normal metals. As the propagation, control and manipulation of the spin currents created in ferromagnets by femtosecond optical pulses is of particular interest, we examine the influence of different thicknesses of the constituent layers for the case of electrons excited several electronvolts above the Fermi level. Using a Monte-Carlo simulation framework for such highly excited electrons, we first examine the spatio-temporal characteristics of the spin current density driven in a Fe layer, where the absorption profile of the light pulses plays an important role. Further, we examine how the combination of light absorption profiles, spin-dependent transmission probabilities, and iron layer thicknesses affect spin current density in a Fe/Au bilayer system. For high-energy electrons studied here, the interface and secondary electron generation have a small influence on spin transport in the bilayer system. However, we find that spin injection from one layer to another is most effective within a certain range of iron layer thicknesses.