Thickness-Dependent Semiconductor-Metal Transition in Two-Dimensional Nonlayered Magnetic CuCo₂S₄

Two-dimensional (2D) magnetic semiconductors that simultaneously host tunable charge transport and robust magnetic order remain scarce because of the intrinsically competing requirements of semiconductivity and magnetism. Here, we report the chemical vapor deposition synthesis of high-quality 2D CuCo₂S₄ nanoflakes and systematically investigate the evolution of their electronic properties as a function of thickness. Owing to dimensional reduction in the nonlayered spinel structure, CuCo₂S₄ undergoes a pronounced metal to semiconductor transition at a critical thickness of ∼20 nm, while long-range ferromagnetic order persists above room temperature. Field-effect transport reveals n-type semiconducting behavior in the thin nanoflakes, in contrast to metallic conduction in thicker counterparts, highlighting thickness-engineered electronic reconstruction. The semiconducting CuCo₂S₄ nanoflakes further exhibit broadband photodetection from visible to near-infrared region with high photoresponse metrics, underscoring the multifunctionality enabled by reduced dimensionality. This work demonstrates dimensional reduction of spinel chalcogenides as an effective strategy for coupling semiconducting transport with robust ferromagnetism.