Spin-voltage-driven efficient terahertz spin currents from the magnetic Weyl semimetals Co$_2$MnGa and Co$_2$MnAl

TL;DR

This study demonstrates that magnetic Weyl semimetals Co$_2$MnGa and Co$_2$MnAl efficiently generate terahertz spin currents upon optical excitation, with potential applications in spintronic devices due to their high efficiency and favorable spin relaxation times.

Contribution

It provides the first experimental evidence of efficient terahertz spin-current generation from magnetic Weyl semimetals, comparing their performance to conventional ferromagnets and offering insights into their spin relaxation dynamics.

Findings

Co$_2$MnGa and Co$_2$MnAl are efficient terahertz spin-current generators.

Spin current relaxation times are comparable to those in Fe.

Magnetic Weyl semimetals show potential as spin-current sources in terahertz spintronics.

Abstract

Magnetic Weyl semimetals are an emerging material class that combines magnetic order and a topologically non-trivial band structure. Here, we study ultrafast optically driven spin injection from thin films of the magnetic Weyl semimetals Co$_2$MnGa and Co$_2$MnAl into an adjacent Pt layer by means of terahertz emission spectroscopy. We find that (i) Co$_2$MnGa and Co$_2$MnAl are efficient terahertz spin-current generators reaching efficiencies of typical 3d-transition-metal ferromagnets such as Fe. (ii) The relaxation of the spin current provides an estimate of the electron-spin relaxation time of Co$_2$MnGa (165 fs) and Co$_2$MnAl (102 fs), which is comparable to Fe (92 fs). Both observations are consistent with a simple analytical model and highlight the large potential of magnetic Weyl semimetals as spin-current sources in terahertz spintronic devices. Finally, our results provide a strategy to identify magnetic materials that provide maximum spin current amplitudes for a given deposited optical energy density.