Coexisting Ferro-Antiferroelectricity in van der Waals NiI2
The pursuit of multiferroic order in atomically thin van der Waals materials faces persistent obstacles: ferroelectricity in the few-layer limit is difficult to confirm alongside magnetic order due to optical technique limitations, and single-phase multiferroics with robust magnetoelectric coupling remain scarce. This highlight examines the work by Bo Peng's group at the University of Electronic Science and Technology of China, who introduced a micro-nano magneto-optical-electric joint measurement scanning imaging technique that combines linear and non-linear tandem capacitance to enhance the area-to-distance ratio in the capacitance plane. Using this platform, they directly observed non-collinear antiferromagnetism and out-of-plane ferroelectricity in trilayer NiI2 through magnetic domains, hysteresis loops, and ferroelectric hysteresis loops. The non-collinear spiral spin configuration generates out-of-plane ferroelectric polarization. Critically, the trilayer NiI2 exhibits unprecedented coexistence of ferroelectricity and antiferroelectricity, with magnetic control over the switching dynamics of ferroelectric domains. This discovery establishes trilayer NiI2 as a platform for probing magnetoelectric coupling at the two-dimensional limit, where electric and magnetic order parameters can be manipulated independently and synergistically. The work represents a significant breakthrough in low-dimensional multiferroics, with potential for ultra-compact spintronic devices and all-electric-field switching.