Thickness‐Dependent Semiconductor‐Metal Transition in Two‐Dimensional Nonlayered Magnetic CuCo ₂ S ₄

ABSTRACT

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 CuCo ₂ S ₄ nanoflakes and systematically investigate the evolution of their electronic properties as a function of thickness. Owing to dimensional reduction in the nonlayered spinel structure, CuCo ₂ S ₄ 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 CuCo ₂ S ₄ 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.