  Spintronic heterostructures are considered to be the new generation THz
sources for their capability in producing high power and broadband THz
radiation. Here, we provide a brief review on the state-of-the-art in this
field. The optically excited bi- and tri-layer combinations of ferromagnetic
and nonmagnetic thin films have become increasingly popular. Towards optimizing
the THz conversion efficiency and broadband gapless spectrum from these THz
emitters, various control parameters need to be taken into consideration. The
inverse spin Hall effect in the heavy metal layer of the heterostructure is
primarily responsible for the generation of THz pulses. A few new results on
iron, platinum and tantalum based heterostructures have also been reported
here. It is observed that the Ta(2nm)/Fe(2nm)/Pt(2nm) tri-layer heterostructure
generates ~40(250)% stronger THz signal as compared to the counterpart
Fe(2nm)/Pt(2nm) (Fe(3nm)/Ta(2nm)) bi-layer heterostructure.
