Influence of Al or Cr substitution on structure and magnetic properties of barium hexaferrites prepared by hydrothermal method

Abstract

In this study, BaFe_12-xCr_xO₁₉ and BaFe_12-xAl_xO₁₉ (x = 0.0, 0.1, 0.3 and 0.4) powders were prepared by a hydrothermal method followed by annealing. The incorporation of Cr and Al in the hexaferrite structure was confirmed by elemental analysis and the results of Rietveld refinement of X-ray diffraction patterns, which revealed a decrease in the lattice volume with increasing x. Based on Mössbauer spectroscopy and magnetic measurements, the lack of Fe³⁺ was observed in the 12k site for BaFe_12-xAl_xO₁₉ samples and in the 12k, 4f₁ and 4f₂ sites for BaFe_12-xCr_xO₁₉ samples. With increasing substitution, the magnetic parameters of Al-substituted hexaferrites varied slightly, possibly due to limited incorporation of Al³⁺. At the same time, a significant decrease in H_c was observed for Cr-substituted samples (5629 Oe for x = 0 and 2092 Oe for x = 0.4). Electron microscopy revealed that the substitution of Fe³⁺ with Al³⁺ had no significant effect on crystallite morphology. The substitution of Fe³⁺ with Cr³⁺ leads to the thinning and widening of the plate-like grains of hexaferrite. This could be one of the reasons for the decrease in coercivity.