Spin-voltage-driven efficient terahertz spin currents from the magnetic Weyl semimetals Co₂MnGa and Co₂MnAl

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 Co2MnGa and Co2MnAl into an adjacent Pt layer by means of terahertz emission spectroscopy. We find that (i) Co2MnGa and Co2MnAl 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 Co2MnGa (165 fs) and Co2MnAl (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

Terahertz-Magnetic-Field Induced Ultrafast Faraday Rotation of Molecular Liquids

Rotation of the plane of the polarization of light in the presence of a magnetic field, known as the Faraday rotation, is a consequence of the electromagnetic nature of light and has been utilized in many optical devices. Current efforts aim to realize the ultrafast Faraday rotation on a sub-picosecond time scale. To this end, the Faraday medium should allow an ultrafast process by which in the presence of an ultrashort intense magnetic field, the light polarization rotates. We meet the criteria by applying an intense single cycle THz mag-netic-field to simple molecular liquids and demonstrate the rotation of the plane of polarization of an optical pulse traversing the liquids on a sub-picosecond time scale. The effect is attributed to the de-flection of an optically induced instantaneous electric polarization under the influence the THz magnetic field. The resolved Faraday rotation scales linearly with the THz magnetic field and quadrati-cally with the molecular polarizability