Structural, optical and magnetic properties of CoAl Fe2-O4 nanoparticles prepared by combustion reaction method

The present study reports on aluminum substituted cobalt ferrite (CoAlxFe2-xO4) nanoparticles (0.00 ≤ x ≤ 2.00) synthesized by combustion reaction method and investigated by transmission electron microscopy, magnetometry, x-ray diffraction, Raman, UV-Vis, and Mossbauer spectroscopies. Within the detection limit of the used techniques, single-phased materials are identified in the whole range of composition (0.00 ≤ x ≤ 2.00). Furthermore, it is observed that the lattice parameter (a) follows the Vegard’s Law, suggesting that the nominal Al3+-ion content (x) effectively replace the Fe3+-ion in the spinel structure. It is observed that the intensity of the diffraction peaks changes as the aluminum content distribution varies. With the help of the Rietveld refinement method and the Mossbauer spectroscopy, this behavior allows one to calculate the cation distribution in A- and B-sites of the spinel structure. The assessed cationic occupation is in excellent agreement with the magnetic measurements data, validating the method herein used to determine the cation’s distribution. Additionally, it is verified that in the transition between inverse to normal spinel, a nearly homogenous redistribution of the remaining Fe3+-ion between A- and B- sites occurs. Magnetization data suggest that the CoAlxFe2-xO4 NPs comprise a homogeneous magnetic core dressed by a spin-glass-like shell. Finally, values of magnetostriction strain sensitivity, much higher than those reported in the literature for the same type of material are estimated in this report, demonstrating that the CoAlxFe2-xO4 NPs constitute promising candidates for applications in stress sensors, actuators, and magnetostrictive filters.