  We fabricated fully epitaxial Fe/ZnO/MgO/Fe magnetic tunnel junctions (MTJs)
with low junction resistance-area products (several $\Omega$ $\mu$m$^2$) and
conducted a theoretical estimation of square-low rectifying performance for a
terahertz electromagnetic wave. Effective current responsivity up to 0.09 A/W
at 1 THz was obtained under zero-bias voltage condition at room temperature.
The result is approximately half the value of the best result obtained for
experiments in semiconductor-based diodes, performed under similar conditions.
The study strongly suggests that this MTJ system has a great potential for the
rectifying element of the terahertz wave.
