Study of Magnetic and Structural Properties of BaFe_12–xCu_xO₁₉ Ferrites Obtained by Hydrothermal Synthesis

Abstract—Hexagonal ferrites of the M-type (in particular, BaFe₁₂O₁₉) are magnetic materials, whose functional characteristics are influenced by both chemical composition and technology of their synthesis. The results of a study of the magnetic and structural properties of hexaferrites BaFe_12–xCu_xO₁₉ (x = 0, 0.1, 0.2, 0.3, and 0.4) with partial substitution of iron by copper obtained using hydrothermal synthesis are presented. The composition of the synthesized samples is analyzed using X-ray phase analysis; magnetic characteristics are measured using a vibrating magnetometer. It is found that the coercive force of the studied powders depends on the copper concentration nonmonotonically and takes maximum (5629 Oe) and minimum (4698 Oe) values at x = 0 and x = 0.2. That is, the presence of copper reduces the coercive force, but its values remain quite high relative to the results of similar studies. With increasing x, the saturation magnetization of the obtained ferrites gradually decreases (from 65.88 to 60.75 A m²/kg at x = 0 and x = 0.4, respectively). The distribution of Cu over the ferrite sublattices is investigated using Mössbauer spectroscopy. It is shown that copper ions preferentially occupy the 12k and 4f₁ positions in the hexaferrite structure. Hence it follows that the decrease in saturation magnetization with increasing x is most likely due to the presence of secondary nonmagnetic phases observed in X-ray diffraction patterns. It is also revealed that during the synthesis process, copper participates in the formation of low-melting phases on the surface of hexaferrite grains, which promotes the agglomeration of particles. This means that the obtained powders can potentially be sintered at lower temperatures and, therefore, without a significant increase in crystallite size. Herewith, the coercive force retains its initial high values. The results can be used to create ferrite permanent magnets with improved characteristics.