Non-van der Waals MCrS2 nanosheets with tunable two-dimensional ferromagnetism

Designing two-dimensional (2D) ferromagnetic materials with high Curie temperature is urgent for the development of spintronic technology. The exploration of non-van der Waals (vdW) ferromagnetic nanosheets play a vital role in enriching the 2D ferromagnetic materials family on account of the scarcity of vdW materials in nature. Herein, we report a non-vdW AgCrS₂ material with antiferro-to-ferro-magnetism transition when it thinned down to monolayer. Based on it, a universal ion-exchange strategy was employed to replace Ag⁺ by the M (M = Li⁺, Na⁺, K⁺) cations, acquiring a series of 2D non-vdW M_xAg_0.5−xCrS₂ materials with tunable ferromagnetism. The Curie temperature is higher than the AgCrS₂ nanosheet, and reaches up to 160 K when M is K⁺. The theoretical calculations verify the ferromagnetism of AgCrS₂ and M_xAg_0.5−xCrS₂ nanosheet originated from CrS₂ layer. The disorderly arranged M and Ag ions increase the asymmetry of the lattice structure of M_xAg_0.5−xCrS₂, thereby strengthening the interlayer ferromagnetic coupling and raising the Curie temperature of the nanosheets. This work provides ideas for discovering more 2D ferromagnetic materials with high Curie temperature.