THz Emission from Exchange-Coupled Fe/Ru/Ni Spintronic Emitters

We explored THz emission from Si/SiO2//Ta/Fe/Ru/Ni/Al2O3 spintronic emitters. We tuned magnetization alignment of Fe and Ni layers by varying the interlayer exchange coupling (IEC) strength using a range of Ru layer thickness t. Depending on IEC strength, magnetization hysteresis shows either ferromagnetic (t = 1.1 nm, 1.5 nm), antiferromagnetic (t = 1.3 nm) or canted (t = 1.7 nm, 1.9 nm) relative alignment. Competition between IEC and an external magnetic field results in a dramatic difference in THz emission from the ferromagnetically (FM) and anti-ferromagnetically (AFM) coupled structures. The resulting THz emission from IEC structures is a result of an interference of THz transiens generated by the individual Fe/Ru and Ru/Ni emitters.