Eco-friendly green synthesis and characterizations of CoFe 2- x Al x O 4 nanocrystals: analysis of structural, magnetic, electrical, and dielectric properties

This work reports, thermal, structural, magnetic, electric, and dielectric investigations of the CoFe 2- x Al x O 4 nanocrystals synthesized through eco-friendly green sol–gel auto-ignition route. X-ray diffractograms exposed the uni-phasic geometry with Fd3m _ O_h^7 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 Al 3+ concentrations, ascribed to the replacement of Fe 3+ ions by paramagnetic Al 3+ 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 Al 3+ ions which is owing to the non-magnetic contamination in the magnetic matrix. The DC-electrical resistivity was enhanced with growing temperature along with Al 3+ content x . The dielectric parameters boosted pointedly with Al 3+ substitution and decline exponentially with a rise in frequency in compliance with ‘Koops’ phenomenological theory. All the outcomes show that Al 3+ 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- x Al x O 4 nanocrystals.