Electrical Control of Terahertz Polarization in an Ultrathin W/FeGa/Pt Spintronic Emitter on PMN-PT

The rigid coupling between the emitted THz polarization and the magnetization orientation of a spintronic emitter enables polarization control, but conventional approaches require tuning an external magnetic field. Here, we demonstrate that in an ultrathin W/FeGa/Pt heterostructure deposited on a PMN-PT (011) substrate, the polarization plane can be smoothly rotated by 40° using a DC voltage alone, under a fixed, weak bias magnetic field (24 Oe). The key element is a 5-nm-thick Galfenol (FeGa) layer sandwiched between heavy metals with opposite signs of the spin Hall angle: it simultaneously serves as the source of the ultrafast spin current and as a magnetostrictive transducer that converts substrate strain into a magnetic response. THz spintronic magnetometry, which probes the structure under the actual conditions of THz generation, allows us to quantitatively correlate the polarization rotation angle with the strain-induced magnetoelastic anisotropy transferred to the film. The obtained results are directed toward the design of compact THz sources with electrically tunable polarization.