Field-free spintronic terahertz emitter with polarization tunability

Abstract

With the rapid expansion of terahertz (THz) applications in next-generation communication systems, imaging technologies, and quantum manipulation, the realization of efficient and highly integrated THz sources that do not rely on complex auxiliary components has emerged as a key challenge. Although spintronic THz emitters have advanced considerably in recent years, most existing schemes still depend on external magnetic fields to stabilize the magnetization orientation, which constitutes a major structural constraint for practical device integration. In this work, we introduce exchange bias into spintronic THz emission by employing a ferromagnetic/antiferromagnetic FeNi/IrMn3 heterostructure, thereby enabling field-free operation of the emitter. Through interfacial exchange coupling, the magnetization of the FM layer is pinned in a well-defined direction, which ensures reliable spin-current injection and spin-to-charge conversion in the absence of an external magnetic field. As a result, robust THz emission can be achieved under zero-field conditions. Beyond eliminating the magnetic field requirement inherent to conventional spintronic THz sources, the incorporation of a stripe-patterned metasurface further allows efficient generation and controllable manipulation of broadband chiral THz waves. A field-free spintronic THz source with controllable polarization state and high efficiency has been achieved.