Actively switchable spintronic terahertz emission with arbitrary polarization states

Flexible manipulation of the polarization state is essential for the practical application of terahertz (THz) waves in many fields. However, the lack of effective, high-quality polarization-tunable THz sources hinders the further development of THz technology. Here, we demonstrate an actively switchable spintronic THz source with polarization states among linear, circular, and elliptical states in the CoFeB/Pt/SiO2(sub)/Ta/Co/IrMn structure by using the antiferromagnet/ferromagnet exchange bias effect, as well as a temporary magnetic field to combine the magnetization directions, and designing the thickness of the substrate to achieve a suitable phase difference. In addition, the chirality, ellipticity, and azimuth of the THz waves can be manipulated arbitrarily by controlling the magnetization combination. More importantly, using rotating motors and electromagnets enables fully automated operations. This highly efficient, polarization-tunable THz source meets most of the existing needs, and its low cost and small size make it more suitable for integration into various devices. It paves the way for accelerating THz spintronic devices and unveiling mechanisms in condensed matter physics.