Switchable ultrafast spintronic THz emitters

T HE recent discovery of ultrafast spintronic THz emitters has attracted a lot of attention due to their high power, broadband emission as well as easy fabrication [1] , [2] . They are based on nanometer-thin bilayers of a magnetic (M) and a nonmagnetic (NM) metal layer and rely on the inverse spin Hall effect. The THz emission properties can be tuned by using different M or NM materials, tailoring the magnetic properties [3] , or building functional layer stacks [4] , [5] . Here, we present a spin valve THz emitter, which allows for switching of the THz emission amplitude by a low magnetic field of a few mT.