  The ability to generate, detect, and control coherent terahertz (THz) spin
currents with femtosecond temporal and nanoscale spatial resolution has
significant ramifications. The diffraction limit of concentrated THz radiation,
which has a wavelength range of 5 {\mu}m-1.5 mm, has impeded the accumulation
of nanodomain data of magnetic structures and spintronic dynamics despite its
potential benefits. Contemporary spintronic optoelectronic apparatuses with
dimensions 100 nm presented a challenge for researchers due to this
restriction. In this study, we demonstrate the use of spintronic THz emission
nanoscopy (STEN), which allows for the efficient injection and precise coherent
detection of ultrafast THz spin currents at the nanoscale. Furthermore, STEN is
an effective method that does not require invasion for characterising and
etching nanoscale spintronic heterostructures. The cohesive integration of
nanophotonics, nanospintronics, and THz-nano technology into a single platform
is poised to accelerate the development of high-frequency spintronic
optoelectronic nanodevices and their revolutionary technical applications.
