Structural, cation distribution, thermal properties, and electrical resistivity of nano NiAlxFe2-xO4 synthesized by flash auto combustion method

Abstract This work reports the effect of Al substitution in Ni ferrite on the structural and electrical resistivity of NiAlxFe2-xO4 (where, x= 0.00, 0.20, 0.40, 0.60, 0.80, and 1.00) nanoparticles synthesized by the flash auto combustion method. The XRD results show the presence of single-phase spinel structure. The average particle size estimated using Debye–Scherer׳s equation and was found to be in the range of 14 – 23.9 nm. Lattice parameter a (A), cell volume and density the studied ferrite NiAlxFe2-xO4 were decreased with increasing Al+3 content. Fe, Al and Ni ions dominantly occupy both tetrahedral (A) and octahedral (B) sites. Occupancy from x=0 to x=1, are changed in A site, from 25%, 8% and 0% to 16% 13% and 6% for Fe, Ni, and Al ions, respectively, and in B site, from 42%, 25% and 0%, to 17% Fe, 22% Ni, 26% for Fe, Ni, and Al ions, respectively. The formation of spinel ferrite confirmed by the two types of stretching vibrations of metal oxide (M-O) bonds. The lower absorption band ʋocta lies in the range of 399-462 cm−1 and the higher absorption band ʋtetra lies in the range of 590-624 cm−1. Mossbauer measurement showed three broad hyperfine magnetic sextets in addition to superparamagnetic doublet were observed in most the measured samples. the component with the higher field value is associated with Fe3+ ions at B- site, while that with smaller field is associated with Fe3+ ions at A-site. The third collapse sextet which have smallest field and very broad width represents an intermediate phase between magnetic and superparamagnetic states. From TGA results, the activation energy of two weight losses are 20.7, 40.6 KJ/mol for Ni-Al ferrite and 14.12, 26.08 KJ/mol for Ni ferrite. The increase of Al content lead to increase in the resistivity from 7.4 to 412 MΩ at room temperature. With increasing temperature, the resistivity of all samples decreased which is a typical semiconductor behavior of ferrites consistent with Verwey hopping model. Curie temperature also increase as Al content increased in range of 353-634 K and in range of 474-577 K for DC and AC respectively. The high electrical resistivity of Ni-Al ferrites makes it preferable to be used in data storage devices