Spintronic THz emitters based on transition metals and semi-metals/Pt multilayers

Heterostructures made of nanometer thick ferromagnetic/heavy metal junctions have become reliable materials in order to achieve broadband and gap-less THz sources, key elements for the development of THz technologies. Whereas the performances of these ultrathin spintronic THz emitters already surpass some usual THz sources, a better understanding of the fundamental emission/absorption mechanisms at play is crucial for reaching higher THz field. Starting from standard bilayer ferromagnetic/transition metal junctions, we present here how THz emission can be significantly enhanced by tailoring the stacking of such structures, adding a spin-sink layer and with the use of semi-metals as spin-injectors. Furthermore, our results allows to extract THz and spin properties of the materials, paving the way towards further enhancement.