Fig. 1. Schematic of spintronic film THz emission with alternating electromagnetic coils.

Fig. 2. (a) Power supply circuit for the electromagnetic coils to produce the alternating magnetic field. (b) Magnetic field versus current and corresponding theoretical calculation for electromagnetic coils.

Fig. 3. (a) Square waveforms detected from the function generator and the oscilloscope. (b) Simplified waveforms for laser modulation by a chopper and electromagnetic field modulation by a function generator. (c) THz signal waveforms from the W/CoFeB/Pt spintronic film measured by a THz emission system, where two reverse directions of the direct current (DC) and alternating current (AC) flow in coils with chopper (w/ chopper) and without chopper (w/o chopper), respectively. (d) THz signal waveforms from the W/CoFeB/Pt spintronic emitter with the original start level (orange line) and a π phase difference start level (gray dash line).

Fig. 4. (a) THz signal waveforms and (b) the peak value of the THz signal under different frequencies from 84 Hz to 6884 Hz. (c) THz signal waveforms and (d) the peak value of the THz signal under different square wave amplitudes from 2 mV to 300 mV.