High performance THz emitters based on ferromagnetic/nonmagnetic heterostructures

Abstract: We report a THz emitter with excellent performances based on nonmagnetic (NM) and ferromagnetic (FM) heterostructures. The spin currents are first excited by the femtosecond laser beam in the NM/FM bilayer, and then transient charge currents are generated by inverse spin Hall effect, leading to THz emission out of the structure. The broadband THz waves emitted from our film stacks have a peak intensity exceeding 500 um thick ZnTe crystals (standard THz emitters). Our device is insensitive to the polarization of an incident laser beam which indicates the noise resistive feature. In contrast, the polarization of THz waves is fully controllable by an external magnetic field. We have also fabricated the devices on flexible substrates with a great performance, and demonstrated that the devices can be driven by low power lasers. Together with the low cost and mass productive sputtering growth method for the film stacks, the proposed THz emitters can be readily applied to a wide range of THz equipment. Our study also points towards an alternative approach to characterize spintronic devices with NM/FM bilayers.