Modelling of Spintronic Terahertz Emitters as a function of spin generation and diffusion geometry

TL;DR

This paper develops a generalized theoretical model using a modified Transfer Matrix Method to analyze how the geometry and material properties of spintronic THz emitters influence their emission efficiency, aiding optimization.

Contribution

It introduces a comprehensive model for spintronic THz emitters that accounts for spin generation, diffusion, and geometry, enabling better design and optimization of these devices.

Findings

Model accurately predicts THz emission as a function of layer thicknesses.

Geometry significantly influences emission amplitude.

Extension to multi-layer configurations is feasible.

Abstract

Spintronic THz emitters (STE) are efficient THz sources constructed using thin heavy-metal (HM) and ferromagnetic-metal (FM) layers. To improve the performance of the STE, different structuring methods (trilayers, stacked bilayers) have been experimentally applied. A theoretical description of the overall THz emission process is necessary to optimize the efficiency of STE. In particular, geometry, composition, pump laser frequency, and spin diffusion will be significant in understanding the pathways for further research developments. This work will apply a generalized model based on a modified Transfer Matrix Method (TMM). We will consider the spin generation and diffusion in the FM and HM layers and explain the spintronic THz emission process. This model is suitable for calculating emitted THz signal as a function of FM and HM thicknesses for different geometrical configurations. We will investigate a bilayer geometry as a test case, but the extension to a multi-layer configuration is straightforward. We will show how the different configurations of the sample will influence the THz emission amplitude.