Mössbauer and Structure-Magnetic Properties Analysis of AB_1-CFe_2-O₄ (C=Ho,Gd,Al) Ferrite Nanoparticles Optimized by...

AB_1-CFe_2-O₄ (C=Ho,Gd,Al) ferrite powders have been synthesized by the sol-gel combustion route. The X-ray diffraction of the CoHoFe_2-O₄ (x = 0~0.08) results indicated the compositions of single-phase cubic ferrites. The saturation magnetisation of CoHoFe_2-O₄ decreased by the Ho³⁺ ions, and the coercivity increased initially and then decreased with the increase of the calcination temperature. The Mössbauer spectra indicated that CoHoFe_2-O₄ displays a ferrimagnetic behaviour with two normal split Zeeman sextets. The magnetic hyperfine field tends to decrease by Ho³⁺ substitution owing to the decrease of the A-B super-exchange by the paramagnetic rare earth Ho³⁺ ions. The value of the quadrupole shift was very small in the CoHoFe_2-O₄ specimens, indicating that the symmetry of the electric field around the nucleus is good in the cobalt ferrites. The absorption area of the Mössbauer spectra changed with increasing Ho³⁺ substitution, indicating that the substitution influences the fraction of iron ions at tetrahedral A and octahedral B sites. The X-ray diffraction of Mg_0.5Zn_0.5CFe_2-O₄(C=Gd,Al) results confirmed the compositions of single-phase cubic ferrites. The variation of the average crystalline size and lattice constant are related to the doping of gadolinium ions and aluminum ions. With increasing gadolinium ions and aluminum ions, the coercivity increased and the saturation magnetization underwent a significant change. The saturation magnetization of AlMg_0.5Zn_0.5FeO₄ ferrite reached a minimum value (M= 1.94 mu/g). The sample exhibited ferrimagnetic and paramagnetic character with the replacement with Gd³⁺ ions, that sample exhibited paramagnetic character with the replacement with Al³⁺ ions, and the isomer shift values indicated that iron is in the form of Fe³⁺ ions.