Tuning 2D Magnetism in Cobalt Monoxide Nanosheets Via In Situ Nickel‐Doping

Element doping has become an effective strategy to engineer the magnetic properties of two‐dimensional (2D) materials and is widely explored in van der Waals layered transition metal dichalcogenides. However, the high‐concentration substitution doping of 2D nonlayered metal oxides, which can preserve the original crystal texture and guarantee the homogeneity of doping distribution, is still a critical challenge due to the isotropic bonding of closed‐packed structures. In this work, the synthesis of high‐quality 2D nonlayered nickel‐doped cobalt monoxide nanosheets via in situ atmospheric pressure chemical vapor deposition method is reported. High‐resolution transmission electron microscopy confirmed that nickel atoms are doped at the intrinsic cobalt atom sites. The nickel doping concentration is stable at ≈15%, superior to most magnetic dopants doping in 2D materials and metal oxides. Magnetic measurements showed that pristine cobalt monoxide is nonferromagnetic, whereas nickel‐doped cobalt monoxide exhibits robust ferromagnetic behavior with a Curie temperature of ≈180 K. Density functional theory calculations reveal that nickel atoms can improve the internal ferromagnetic correlation, giving rise to significant ferromagnetic performance of cobalt monoxide nanosheets. These results provide a valuable case for tuning the competing correlated states and magnetic ordering by substitution doping in 2D nonlayered oxide semiconductors. The synthesis of two‐dimensional (2D) nickel‐doped cobalt monoxide (Ni‐doped CoO) nanosheets with a high substitution doping concentration is proposed for the first time. 2D Ni‐doped CoO exhibits obvious ferromagnetism with a Curie temperature of ≈180 K, in sharp contrast to the pristine non‐ferromagnetic 2D CoO, opening up a prospective way for tuning the magnetism of 2D nonlayered oxide semiconductors.