2D free-standing ultra-large ferromagnetic nanosheets via a topotactic transformation strategy

Considerable progress has been made in synthesizing two-dimensional（2D） materials by exfoliating layered solids.However,for tremendous non-layered inorganic materials,especially magnet solids,usually with closely packed bulk phases by strong chemical bonds,it is challenging to obtain their high-quality 2D sheets.Herein,we highlighted a new structure of free-standing ferromagnetic nanosheets featuring（111） facets.For magnet,Fe3O4,its inversed spinel crystalline has limited abilities to exfoliate into 2D forms and rarely exists as free-standing nanosheets owing to aggregation induced by magnetic force.We realized a breakthrough in achieving free-standing ferromagnetic nanosheets with dramatically surpassing size limitations via topotactic conversion from layered counterparts.Our Fe3O4 nanosheets exhibited a maximum width of 60μm while only～4 nm thick,prominently exposing（111） facets.2D Fe3O4 behaved anisotropic magnetism,which displayed a 4.6 emu g-1 moment（H=500 Oe） in the（111） plane but 2.1 emu g-1out of the（111） plane,indicating a（111） in-plane easy axis.We anticipated our topotactic conversion strategy would inspire the creation of 2D non-layered materials and enrich the 2D materials family.