  In this work, we report our study on the THz emission in Fe/Pt magnetic
heterostructures. We have carried out a comprehensive investigation of THz
emission from Fe/Pt magnetic heterostructures, employing time-domain THz
spectroscopy. We reveal that by properly tuning the thickness of Fe or Pt
layer, THz emission can be greatly improved in this type of heterostructure. We
further demonstrate that the THz field strength emitted from a newly designed
multilayer (Pt/Fe/MgO)$_n$ with n=3 can reach a value of ~1.6 kV/cm, which is
comparable to the values from the conventional GaAs antenna with a bias of 4
kV/cm, and the nonlinear crystals, e.g., 100 micrometer GaP and 2 mm ZnTe. For
the first time, the intensity and spectrum of THz wave is demonstrated to be
tunable by the magnetic field applied on the patterned magnetic Fe/Pt
heterostructures. These findings thus promise novel approaches to fabricate
powerful and tunable THz emitters based on magnetic heterostructure.
