Controllable defect-induced room temperature ferromagnetism in single-layered titanium oxide nanosheets

We investigated defect-induced ferromagnetism of titanium oxide nanosheets, one of the thinnest two-dimensional (2D) oxide materials obtained by chemical exfoliation from layered titanate. Magnetization measured for single-layered titanium oxide nanosheets shows ferromagnetic behavior at room temperature, which is attributable to native defects generated during the exfoliation process. The ferromagnetism can be controlled by further introducing defects by Ar⁺ion irradiation. The saturation magnetization is found to non-monotonically vary with the fluences of irradiated Ar⁺ions with an energy of 200 eV. Electron diffraction patterns reveal that the mild irradiation does not change the initial lepidocrocite structure. X-ray photoemission spectroscopy measurements show a slight shift in the binding energy of Ti atoms with a valence of +4. X-ray absorption near edge structure spectra reveal the modification of the electronic structure by the further introduction of defects. The stable and controllable ferromagnetism at room temperature in the ultra-thin titanium oxide nanosheets can be an indispensable piece for future spintronics devices consisting of 2D materials.