Effect of Al⁺³ substitution on optical, magnetic, and ferroelectric properties of hematite (α-Al_xFe_2−xO₃) nanostructures

In this work, pure and Al-doped hematite (α-Al_xFe_2−xO₃) nanostructures were synthesized to investigate the structural, optical, magnetic, and ferroelectric properties. The analysis of X-ray diffraction data through Rietveld refinement elucidates the stabilization of both compounds within the hexagonal R3c symmetry. Raman analysis reveals that the spectral characteristics of the hematite structure fluctuate due to local disorder caused by the introduction of Al³⁺ ions into the Fe(O)₆ octahedra. The morphological investigation performed with FESEM and TEM indicates a spherical-like shape of the nanostructures. The absorption edges have shifted towards longer wavelengths and reduced optical bandgaps with the lowest bandgap of 1.88 eV observed in Al_0.60Fe_1.40O₃. Significant enhancements in the refractive index (n), extinction coefficient (k), as well as the real and imaginary dielectric constants of hematite nanostructures were obtained in (α-Al_xFe_2−xO₃) system, as calculated via spectrophotometric analysis. The enhanced magneto-crystalline anisotropy observed in Al-doped hematite nanostructures results in elevated coercivity accompanied by pronounced indications of remanence. Notably, the identification of a singular contour in the FORC diagram of Al_0.20Fe_1.8O₃ signifies the presence of a distinct magnetic phase. P-E loops reveal the existence of spontaneous ferroelectric polarization with enhanced remnant polarization making (α-Al_xFe_2−xO₃) system a potential candidate for spintronics, opto-magnetic, high-capacity data storage, and eco-friendly photocatalysis for sustainable energy endeavors.