Roles of Cr termination and Cr vacancy layer in Tuning the Magnetic and Electronic Properties of Non-Layered Cr₂Se₃: first principles study

The electronic and magnetic behaviors of two-dimensional (2D) non–van der Waals Cr₂Se₃ materials are strongly influenced by surface terminations, thickness variations, and the response of the internal vacancy layer. Using first-principles density functional theory calculations, we systematically investigated electronic and magnetic properties of bulk and 2D layered Cr₂Se₃ structures to understand these effects. Bulk Cr₂Se₃ exhibits ferrimagnetic ordering with half-metallic characteristics. Layered structures, on the other hand, strongly depend on surface terminations (e.g., Se/Se, Cr/Se, and Cr/Cr) and layer thicknesses (e.g., 1L–6L). Our results show that most Cr/Se and Cr/Cr terminated 2D Cr₂Se₃ films preserve half-metallicity (except for a tiny gap of ~0.1 eV in 1L Cr/Se) and ferromagnetic ordering up to six layers. The turning from the ferrimagnetic to ferromagnetic is correlated to the vacancy-layer expansion-induced alignment in spin polarization. In contrast, Se/Se-terminated systems maintain bulk-like magnetic behavior but evolve from half-metallic to metallic character. This transition arises from vacancy-layer compression, which enhances Se–Se hybridization and drives metallicity. These findings highlight the crucial role of Cr termination and Cr vacancy-layer engineering in tuning the magnetism and electronic structure of non-layered Cr₂Se₃, offering valuable guidance for designing 2D spintronic and nanoscale devices.