Bottom-Up Synthesis of Co_xSn_1−xS Nanosheets: A Ferromagnetic and Photoconductive Semiconductor

2D ferromagnetic semiconductors are key to next-generation spintronic devices in the post-Moore era. The combination of ferromagnetic and optoelectronic properties offers exciting opportunities for advanced multifunctional devices in spin-optoelectronic applications. Herein, the authors synthesize 2D van der Waals (vdW) Co_xSn_1-xS with ferromagnetism and photoresponse through a bottom-up reaction, which has a high yield compared to typical mechanical exfoliation. Ferromagnetic ordering is realized in 2D vdW semiconductor SnS by Co doping at the Sn sites. Magnetic properties are thoroughly studied at different doping concentrations, and first-principles calculations are further performed to reveal the magnetism origin and spin interactions. In particular, a low Gilbert damping of 1.69 × 10⁻³ is obtained in vdW Co_xSn_1−xS through ferromagnetic resonance. In addition, photodetectors based on Co_xSn_1−xS quantum dots are demonstrated. These studies establish a promising semiconductor with both ferromagnetic ordering and photoelectric response, which provides unprecedented opportunities in spintronic-photonic integrated applications.