Fully reversible magnetoelectric voltage controlled THz polarization rotation in magnetostrictive spintronic emitters on PMN-PT

THz polarization control upon generation is a crucially missing functionality. THz spintronic emitters based on the inverse spin Hall effect allow for this by the strict implicit orthogonality between their magnetization state and the emitted polarization. This control was up till now only demonstrated using cumbersome external magnetic field biasing to impose a polarization direction. We present here for the first time an efficient voltage control of the polarization state of terahertz spintronic emitters. Using a ferromagnetic spin pumping multilayer exhibiting simultaneously strong uniaxial magnetic anisotropy and magnetostriction in a crossed configuration, an emitter is achieved where in principle the stable magnetization direction can be fully and reversibly controlled over a 90$^\circ$ angle span only by an electric voltage. To achieve this, an engineered rare-earth based ferromagnetic multilayer is deposited on a piezoelectric $\textrm{(1-x)[Pb(Mg}_\textrm{0.33}\textrm{Nb}_\textrm{0.66})\textrm{O}_\textrm{3}\textrm{]-x[PbTiO}_\textrm{3}\textrm{]}$ (PMN-PT) substrate. We demonstrate experimentally a reversible 70$^\circ$ THz polarization rotation by sweeping the substrate voltage over 400V. This demonstration allows for a fully THz polarization controlled ISHE spintronic terahertz emitter not needing any control of the magnetic bias.