Spin-polarized hot electron transport versus spin pumping mediated by local heating

TL;DR

This paper presents a simplified model comparing spin-polarized hot electron transport and spin pumping due to local heating in laser-excited magnetic heterostructures, highlighting the dominance of spin pumping in generated spin currents.

Contribution

The paper introduces a toy model that captures the essential physics of both spin-polarized hot electron transport and spin pumping, providing insights into their relative contributions.

Findings

Spin pumping dominates the spin current in the model.

Hot electron spin current is relatively small.

The ratio of Fermi to Curie temperature influences the contributions.

Abstract

A `toy model' - aimed at capturing the essential physics - is presented that jointly describes spin-polarized hot electron transport and spin pumping driven by local heating. These two processes both contribute to spin-current generation in laser-excited magnetic heterostructures. The model is used to compare the two contributions directly. The spin-polarized hot electron current is modeled as one generation of hot electrons with a spin-dependent excitation and relaxation scheme. Upon decay, the excess energy of the hot electrons is transferred to a thermalized electron bath. The elevated electron temperature leads to an increased rate of electron-magnon scattering processes and yields a local accumulation of spin. This process is dubbed as spin pumping by local heating. The built-up spin accumulation is effectively driven out of the ferromagnetic system by (interfacial) electron transport. Within our model, the injected spin current is dominated by the contribution resulting from spin pumping, while the hot electron spin current remains relatively small. We derive that this observation is related to the ratio between the Fermi temperature and Curie temperature, and we show what other fundamental parameters play a role.