Direct electrical control of a single-layer multiferroic

Two-dimensional (2D) magnetic van der Waals materials can exhibit novel phases that are not present in bulk materials due to reduced dimensionality. Among them, type-II 2D multiferroics are of unique interest because of the coexistence of a helical magnetic ground state, a magnetism-induced ferroelectric order, and a record-strength magnetoelectric coupling. Following the recent discovery of single-layer multiferroic in NiI2 system, here we study the magnetic ground state of single-layer NiI2 as a function of electrostatic doping and electric field in a dual gate device architecture. The evolution of magnetic and ferroelectric orders is investigated using magneto-optical Kerr effect microscopy, circularly dichroic Raman spectroscopy, and second-harmonic generation. Specifically, we investigated the helimagnetic transition temperature, the spin helix chirality, and the propagation direction and periodicity of the spin helical vector as a function of electrostatic doping and electric field. This work aimed for the piloting attempt of direct electrical control of a single-layer multiferroic system. These observations provide a new platform for studying 2D magnetism, chiral magnetic textures, and magnetoelectric coupling, yielding transformative technological potentials such as low-power nanoelectronic devices.