Otimização dos parâmetros da síntese do método de reação no estado sólido assistido por moagem de alta energia na hexaferrita de estrôncio dopada com Co2+ e Sn4+

Abstract

In this study, the synthesis parameters of the conventional solid-state reaction combined with high-energy milling were optimized to obtain a monophase hexaferrite compound at lower temperatures, without secondary phases. Two methods were proposed: the conventional solid-state reaction and the solid-state reaction assisted by high-energy milling, with an excess addition of strontium (Sr) ions. A comparison between these two methods was conducted. Samples synthesized by the first method were characterized using techniques such as X-ray diffraction and Rietveld refinement, scanning electron microscopy, energy dispersive spectroscopy, and Mössbauer spectroscopy. Additionally, the magnetic properties were investigated using a vibrating sample magnetometer, analyzing the effects of doping Co2+ and Sn4+ ions in the (SrFe12−2x(CoSn)xO19 system, with (0.0 ≤ x ≤ 0.7), at room temperature. The results showed a slight increase in the lattice parameters ’a’ and ’c’ with the increase in Co2+ and Sn4+ content. The refinement of atomic positions revealed minor modifications in the Fe3+ ion positions and more significant variations in the O3 and O4 ion positions, indicating the substitution of dopants in nearly all Fe ion sites. Quantitative phase analysis revealed the presence of several secondary phases in compositions with higher Co-Sn content, including hematite at low concentrations and magnetite at high concentrations. Mössbauer spectroscopy confirmed the insertion of Co2+ and Sn4+ dopants into the (2b, 4f1, 4f2, 12k sites of Fe3+. The morphological analysis of the samples revealed platelet-like particles with irregular sizes and a tendency to agglomerate due to their magnetic nature. The particle diameter increased from 0.93 μm in pure hexaferrite to 1.13 μm in the most doped sample. EDS analysis confirmed the increasing presence of Co and Sn. Regarding magnetic measurements, a decrease in coercivity (Hc) and magnetocrystalline anisotropy (Keff) was observed with increasing Co2+ and Sn4+ content. In the second method, synthesis was carried out using solid-state reaction assisted by high-energy milling for times ranging from 1 to 9 hours with the addition of 0.4% excess Sr. Samples were characterized by X-ray diffraction and Rietveld refinement, revealing the presence of a single hexaferrite phase in all compositions with (0.0 ≤ x ≤ 0.7) for 9 hours of milling. There was an increase in the lattice parameters ’a’ and ’c’ as the compositions increased. Furthermore, the material’s structural stability was maintained, demonstrating that the solid-state reaction method assisted by high-energy milling is effective in preventing the formation of secondary phases and promoting doping homogeneity.