Ferromagnetism in 2D α-Fe2O3 nanosheets

Abstract

In this report, hematene (2D α-Fe₂O₃ nanosheets) with an exceptionally high coercivity of up to 7.5 kOe has been synthesized via a soft-chemical exfoliation process. The high coercivity correlates with the surface magnetic anisotropy that originates from enhanced uncompensated spin canting as a result of the 2D morphology. This observation is different from the behavior of the bulk counterpart that exhibits collinear antiferromagnetic ordering with no net magnetization at low temperatures. In addition, our study shows a suppression of the Morin transition in 2D nanosheets, which further confirms that the surface spins deviate strongly from the collinear antiferromagnetic ordering. We also observed a spin-glass-like transition with a rapid increase in saturation magnetization and a decrease in anisotropy in the ultra-thin α-Fe₂O₃ nanosheets at temperatures below 48 K. The spin-glass behavior is correlated with the observed exchange bias and the magnetic field dependence of spin-glass freezing temperature.