Exchange-Coupled Spintronic Emitters for Tunable THz Emission Control

We investigated THz emission from Si/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>//Ta/Fe/Ru/Ni/Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> and MgO//Pt/Fe/Cr/Fe/Pt spintronic emitters. In the first emitter a single Ru metallic (NM) layer controls both the interlayer exchange coupling (IEC) and the spin-to-charge conversion (SCC) whereas in the second emitter, IEC and SCC are defined separately by Cr and Pt layers. By varying the Ru and Cr spacer thicknesses we tuned the IEC strength, thereby controlling the magnetization alignment of the ferromagnetic (FM) layers. Depending on the IEC, FM magnetizations exhibit parallel, antiparallel, or canted configurations. The laser-induced THz emission results from constructive or destructive interference of THz transients generated at the two closely spaced FM/M interfaces.