Dimensionality‐Driven Metal‐to‐Insulator Transition in Two‐Dimensional Antiferromagnetic R‐Cr ₂ Se ₃

ABSTRACT 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‐)Cr 2 Se 3 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‐Cr 2 Se 3 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.