Half-Unit-Cell α-Fe_2O_3 Semiconductor Nanosheets with Intrinsic and Robust Ferromagnetism

摘要

The synthesis of atomically thin transition-metal oxide nanosheets as a conceptually new class of materials is significant for the development of next-generation electronic and magnetic nanodevices but remains a fundamental chemical and physical challenge. Here, based on a "template-assisted oriented growth" strategy, we successfully synthesized half-unit-cell nanosheets of a typical transition-metal oxide α-Fe_2O_3 that show robust intrinsic ferromagnetism of 0.6 μ_B/atom at 100 K and remain ferromagnetic at room temperature. A unique surface structure distortion, as revealed by X-ray absorption spectroscopy, produces nonidentical Fe ion environments and induces distance fluctuation of Fe ion chains. First-principles calculations reveal that the efficient breaking of the quantum degeneracy of Fe 3d energy states activates ferromagnetic exchange interaction in these Fe_(5-co)-O-Fe_(6-co) ion chains. These results provide a solid design principle for tailoring the spin-exchange interactions and offer promise for future semiconductor spintronics.