Cr–Mg co-doped Al2O3 nanoparticles synthesized via ball milling: structural, optical, and magnetic properties

In the present study, pure Al 2 O 3 and Cr–Mg co-doped Al 2 O 3 nanoparticles, whose formula is Al 2−(x+y) Cr x Mg y O 3 ( x , y = 0.05 and 0.07). All samples were prepared using a high-energy ball-milling (HEBM) technology to investigate their structural, morphological, optical, and magnetic characteristics. Cr–Mg co-doped samples were subjected to heat treatment at 1100 °C to examine their physical characteristics. They possessed a crystalline γ-Al 2 O 3 phase in the pure form, according to the X-ray diffraction (XRD) phase analysis. The pure and Cr–Mg co-doped samples transitioned into the α-Al 2 O 3 phase at a steady temperature of 1100 °C. Furthermore, the X-ray diffraction patterns of the co-doped samples showed no extra peaks. TEM images revealed that the nanoparticles formed agglomerates of ~ 200 nm, whereas HRTEM confirmed that the individual primary particles were significantly smaller. As validated by the energy dispersive X-ray examination (EDS), the elemental composition of Al, O, Cr, and Mg was close to the predicted atomic ratio. In terms of optical bandgap, the ultraviolet diffuse-reflectance spectroscopy (UV-DRS) tests revealed that when the Cr–Mg concentration increased, the bandgap shrank from 4.301 to 4.173 eV. Results from the vibrating sample magnetometer (VSM) indicated that at room temperature (RT), doped samples’ magnetic behavior shifted to a paramagnetic state. The saturation magnetization rose as the dopant concentration increased, from 0.1081 to 0.12745 emu/g. The multifunctional characteristics of Al 2 O 3 nanoparticles may be efficiently tailored by doping and thermal treatment, as these data demonstrate. Al 2 O 3 metal oxide semiconductors are extensively employed due to their many applications in optical and electrical domains and their good characteristics.