Defect engineering has been utilized to induce ferromagnetism in various nonmagnetic van der Waals (vdW) crystals, which are vital for fundamental research and applications. Herein, oxygen vacancies were successfully created in montmorillonite, a layered aluminosilicate, by acetic acid treatment and annealing in an argon atmosphere. This treatment facilitated the transition from paramagnetism to room-temperature ferromagnetism with a Curie temperature of 330 K. As the annealing temperature increased, in-plane stretching along the [002] crystallographic direction was found to reduce the formation energy of oxygen defects, thereby promoting the creation of oxygen vacancies. By controlling the concentration of oxygen vacancies, precise regulation of the material's ferromagnetic properties was achieved. This work presents a novel room-temperature ferromagnetic material and advances the study of oxygen vacancy-induced ferromagnetism in vdW materials.
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