Interface reflectivity of a superdiffusive spin current in ultrafast demagnetization and THz emission

TL;DR

This paper investigates how spin-dependent interface reflectivity influences ultrafast demagnetization and terahertz emission in ferromagnet/nonmagnet bilayers, revealing that interface engineering can significantly enhance THz radiation.

Contribution

It introduces a first-principles method to calculate spin-dependent interface reflectivity and demonstrates its impact on ultrafast spin dynamics and THz emission in bilayer systems.

Findings

Spin-dependent reflection affects ultrafast demagnetization.

Spin filtering at Fe|NM interfaces enhances spin current.

Interface tailoring can optimize THz emission.

Abstract

The spin- and energy-dependent interface reflectivity of a ferromagnetic (FM) film in contact with a nonmagnetic (NM) film is calculated using a first-principles transport method and incorporated into the superdiffusive spin transport model to study the femtosecond laser-induced ultrafast demagnetization of Fe|NM and Ni|NM (NM= Au, Al & Pt) bilayers. By comparing the calculated demagnetization with transparent and real interfaces, we demonstrate that the spin-dependent reflection of hot electrons has a noticeable influence on the ultrafast demagnetization and the associated terahertz electromagnetic radiation. In particular, a spin filtering effect is found at the Fe|NM interface that increases the spin current injected into the NM metal, which enhances both the resulting demagnetization and the resulting THz emission. This suggests that the THz radiation can be optimized by tailoring the interface, indicating a very large tunability.