Mössbauer and Structure-Magnetic Properties Analysis of A(y)B(1−y)C(x)Fe(2−x)O(4) (C=Ho,Gd,Al) Ferrite Nanoparticles Optimized by Doping

A(y)B(1−y)C(x)Fe(2−x)O(4) (C=Ho,Gd,Al) ferrite powders have been synthesized by the sol-gel combustion route. The X-ray diffraction of the CoHo(x)Fe(2−x)O(4) (x = 0~0.08) results indicated the compositions of single-phase cubic ferrites. The saturation magnetisation of CoHo(x)Fe(2−)(x)O(4) decreased by the Ho(3+) ions, and the coercivity increased initially and then decreased with the increase of the calcination temperature. The Mössbauer spectra indicated that CoHo(x)Fe(2−)(x)O(4) displays a ferrimagnetic behaviour with two normal split Zeeman sextets. The magnetic hyperfine field tends to decrease by Ho(3+) substitution owing to the decrease of the A–B super-exchange by the paramagnetic rare earth Ho(3+) ions. The value of the quadrupole shift was very small in the CoHo(x)Fe(2−x)O(4) 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 Ho(3+) substitution, indicating that the substitution influences the fraction of iron ions at tetrahedral A and octahedral B sites. The X-ray diffraction of Mg(0.5)Zn(0.5)C(x)Fe(2−x)O(4)(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(0.5)Zn(0.5)FeO(4) ferrite reached a minimum value (M(S) = 1.94 mu/g). The sample exhibited ferrimagnetic and paramagnetic character with the replacement with Gd(3+) ions, that sample exhibited paramagnetic character with the replacement with Al(3+) ions, and the isomer shift values indicated that iron is in the form of Fe(3+) ions.