Eco-friendly green synthesis and characterizations of CoFe_2-x Al_xO₄ nanocrystals: analysis of structural, magnetic, electrical, and dielectric properties

Abstract: This work reports, thermal, structural, magnetic, electric, and dielectric investigations of the CoFe_2-xAl_xO₄ nanocrystals synthesized through eco-friendly green sol–gel auto-ignition route. X-ray diffractograms exposed the uni-phasic geometry with Fd3m^_Oh7 space group. The standard crystallite sizes were found in between 24 and 44 nm, confirming the nano-crystalline dimension. FTIR analysis confirmed the two specific vibrational stretching bands corresponding to the spinel ferrite geometry. The surface topology of ferrite nanocrystals with size distribution was effectively observed from TEM micrographs. The magnetic study at room temperature showed lessening in saturation magnetization with rise in Al³⁺ concentrations, ascribed to the replacement of Fe³⁺ ions by paramagnetic Al³⁺ ions. The M–H loops showed the perfect loop of typical soft ferromagnetic behavior of the produced nano-ferrites. The saturation magnetization, coercivity, and magneto-crystalline anisotropy declines with the upsurge in Al³⁺ ions which is owing to the non-magnetic contamination in the magnetic matrix. The DC-electrical resistivity was enhanced with growing temperature along with Al³⁺ content x. The dielectric parameters boosted pointedly with Al³⁺ substitution and decline exponentially with a rise in frequency in compliance with ‘Koops’ phenomenological theory. All the outcomes show that Al³⁺ substitution influences the physical characteristics of cobalt ferrite nanocrystals which shows its suitability in various technological applications. Graphic abstract: The graphical abstract presenting the synthesis reaction, TEM micrograph (along with crystallite size distribution) and M–H plots for CoFe_2-xAl_xO₄ nanocrystals. [Figure not available: see fulltext.]