Supercritical CO₂-induced room-temperature ferromagnetism in two-dimensional MoO_3−x

Two-dimensional (2D) magnetic semiconductors are crucial in spin-based information-processing technologies due to the combination of the strong 2D quantum effects, surface effects and the control of spin states. However, most experimental approaches for tuning 2D magnets achieve pure ferromagnetism at low temperature. Herein, a defect engineering strategy using supercritical CO₂ is introduced to achieve nanostructure with abundant defects for 2D MoO_3−x, and room-temperature ferromagnetism can be obtained and tuned by introduction of the Mo⁵⁺ ion depending on the change of supercritical pressure. In defective regions, the presence of the pentacoordinated [Mo⁵⁺O₅] centers can achieve ferromagnetic ordering resulting in room-temperature ferromagnetism. With increasing supercritical pressure, it is easier for the supercritical CO₂ to break the Mo–O bonds, achieving enhancement of the ferromagnetic performance with desired Curie temperature (>380 K). The magnetic responses in the MoO_3−x system provide a step closer to the expansion of spin electronics.