Structural and magnetic properties of Ni-doped yttrium iron garnet nanopowders

We present a study about the structural and magnetic properties of Ni-doped yttrium iron garnet nanopowders synthesized by sol-gel. The Rietveld refinement of the X-ray diffractograms indicates the replacement of Fe by Ni in the tetrahedral (d) and octahedral (a) sites of yttrium iron garnet (YIG) structure. The lattice parameter showed variation associated to the effects of Ni inclusion and structural defects, such as, oxygen vacancies. The morphological analysis evidence particles with a cylindrical shape and the Energy Dispersive Spectroscopy results corroborate the presence of Ni. The average porosity suggests that the replacement of Fe by Ni does not substantially change the textural properties of the particles. The Fourier transform infrared and Raman spectroscopies showed the characteristic absorption bands of YIG and confirmed the substitution in the a-sites and dsites. The saturation magnetization was studied from the hysteresis loops measurements and present variations with the dopant concentration, associated to the replacement of Fe by Ni and to the oxygen vacancies occurrence. Changes in the coercive field for different dopant concentration were associated to the particle size and pinning centers existence.