Rietveld structure refinement, cation distribution and magnetic properties of Al3+ substituted NiFe2O4 nanoparticles

Ferrite samples of Al3+ substituted NiFe2O4 nanoparticles were prepared by wet chemical co-precipitation method. The samples were obtained by annealing at relatively low temperature at 600 degrees C and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), and ac susceptibility. On applying the full pattern fitting of Rietveld method using FullProf program, exact coordinates of atoms, unit cell dimensions, atom ion occupancy, degree of inversion as well as crystallite size and residual microstrain have been determined. The lattice parameter, density, particle size, lattice strain, magnetization, magneton number, and Curie temperature are seen to decrease with increasing Al3+ content whereas the specific surface area, porosity, coercive force, shows an increasing trend with Al3+ content. Cation distribution is obtained from XRD and Rietveld method and the variation of the cation distribution has been discussed on the basis of site preference, size and valence of the substituting cations. The variation of the magneton number with the Al3+ content is satisfactorily explained on the basis of Neel's collinear spin ordering model. Curie temperature of all the compositions are also obtained theoretically and it agrees with observed Curie temperature. (C) 2011 American Institute of Physics. [doi:10.1063/1.3559266]