Dimensionality-Driven Metal-to-Insulator Transition in Two-Dimensional Antiferromagnetic R-Cr₂Se₃

The integration of magnetism and semiconductivity in a single material remains a central challenge in condensed matter physics, as conventional approaches struggle to reconcile the competing requirements of a finite bandgap and robust magnetic ordering. Here, we report a complementary strategy that inverts the traditional design logic: starting from a magnetic metal, we induce a controlled metal-to-insulator transition (MIT) through dimensionality reduction in two-dimensional (2D) layers. Using rhombohedral (r-)Cr₂Se₃ as a model system, we show that thinning from bulk to atomically thin nanosheets progressively opens a bandgap while preserving antiferromagnetic ordering. Transport measurements reveal a pronounced thickness-dependent crossover from metallic to semiconducting behavior, driven primarily by quantum confinement under dimensional reduction, while the effects of external magnetic and electric fields remain minor. Supported by first-principles calculations, our results establish r-Cr₂Se₃ as a rare non-van der Waals 2D antiferromagnetic semiconductor and illustrate that dimensionality-driven MIT offers a viable pathway for engineering robust 2D magnetic semiconductors, providing a new platform for spintronic and multifunctional device applications.