Abstract
Hexagonal ferrites of M-type (in particular, BaFe12O19) are magnetic materials with functional characteristics affected both by chemical composition and technology of their synthesis. We present the results of studying the magnetic and structural properties of BaFe12 – xCuxO19 hexaferrites (x = 0, 0.1, 0.2, 0.3, 0.4) obtained by hydrothermal synthesis with partial substitution of copper for iron. The composition of the synthesized samples was analyzed using X-ray diffraction, and the magnetic characteristics were measured using a vibration magnetometer. It has been revealed that the coercivity of the ferrite powders depends non-monotonically on the copper concentration and reaches the maximum (5629 Oe) and minimum (4698 Oe) values at x = 0 and x = 0.2. The presence of copper reduces the coercive force, but at the same time the values remain rather high compared to the results of similar studies. 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) with increasing. The distribution of Cu over ferrite sublattices was studied using Mössbauer spectroscopy. It is shown that in the hexaferrite structure, copper ions preferentially occupy 12k and 4f1 sites. Hence, a decrease in the saturation magnetization with increasing x is most likely attributed to the presence of side non-magnetic phases observed on X-ray diffraction patterns. It is also revealed that during synthesis, copper participates in the formation of low-melting phases on the surface of hexaferrite grains which promotes agglomeration of the particles. Thus, the resulting powders can potentially be sintered at lower temperatures and, therefore, without a significant increase in the size of crystallites. Herewith, the coercivity retains its original high values. The results obtained can be used in developing ferrite permanent magnets with improved characteristics.
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