Ultrafast magnetization enhancement and spin current injection in magnetic multilayers by exciting the nonmagnetic metal

TL;DR

This paper investigates how exciting nonmagnetic metals in Au/FM multilayers can generate ultrafast, highly spin-polarized currents, revealing the importance of interface properties and multilayer design for future spintronics.

Contribution

It introduces a theoretical framework for understanding spin injection and demonstrates how multilayer structure optimization enhances spin current generation.

Findings

Spin injection depends on interface reflectivity of hot electrons.

Ultrafast spin currents can be significantly enhanced by multilayer design.

Optimizing layer thickness and stacking improves spin polarization and current intensity.

Abstract

A systematic investigation of spin injection behavior in Au/FM (FM = Fe and Ni) multilayers is performed using the superdiffusive spin transport theory. By exciting the nonmagnetic layer, the laser-induced hot electrons may transfer spin angular momentum into the adjacent ferromagnetic (FM) metals resulting in ultrafast demagnetization or enhancement. We find that these experimental phenomena sensitively depend on the particular interface reflectivity of hot electrons and may reconcile the different observations in experiment. Stimulated by the ultrafast spin currents carried by the hot electrons, we propose the multilayer structures to generate highly spin polarized currents for development of future ultrafast spintronics devices. The spin polarization of the electric currents carried by the hot electrons can be significantly enhanced by the joint effects of bulk and interfacial spin filtering. Meanwhile the intensity of the generated spin current can be optimized by varying the number of repeated stacking units and the thickness of each metallic layer.