Terahertz Emission From an Exchange-Coupled Synthetic Antiferromagnet

We report on terahertz emission from Fe-Mn-Pt/Ru/Fe-Mn-Pt and Pt/Co-Fe-B/Ru/Co-Fe-B/Pt synthetic antiferromagnet (SAF) structures upon irradiation by a femtosecond laser; the former is via the anomalous Hall effect, whereas the latter is through the inverse spin Hall effect. The antiparallel alignment of the two ferromagnetic layers leads to a terahertz emission peak amplitude that is almost double that of a corresponding single-layer or bilayer emitter with the same equivalent thickness. In addition, we demonstrate by both simulation and experiment that terahertz emission provides a powerful tool to probe the magnetization reversal processes of individual ferromagnetic layers in a SAF structure, as the terahertz signal is proportional to the vector difference (M-1 - M-2) of the magnetizations of the two ferromagnetic layers.