  Ultrafast THz radiation generation from ferromagnetic/nonmagnetic bilayer
heterostructure-based spintronic emitters generally exploits the conversion
from spin- to charge-current within the nonmagnetic layer and its interface
with the ferromagnetic layer. Various possible sub-contributions to the
underlying mechanism of inverse spin Hall effect for the THz emission from such
structures, need to be exploited for not only investigating the intricacies at
the fundamental level in the material properties themselves but also for
improving their performance for broadband and high-power THz emission. Here, we
report ultrafast THz emission from CoFeB/Ta bilayer at varying sample
temperatures in a large range to unravel the role of intrinsic and extrinsic
spin to charge conversion processes. In addition to an enhancement in the THz
emission, its temperature dependence shows a THz signal polarity reversal if
the CoFeB/Ta sample is annealed at an elevated temperature. We extract the
behaviour of the spin Hall resistivity, determine the intrinsic spin Hall
conductivity contribution in it and compare those with the standard Fe/Pt
system. Our results clearly demonstrate a giant interfacial contribution to the
overall spin Hall angle arising from the modified interface in the annealed
CoFeB/Ta, where a sign reversal in the corresponding spin Hall angle is
manifested from the THz amplitude variation with the temperature.
