Cr-substituted M-type hexaferrite solid solutions with high level of substitution

Objectives. This study aims to synthesize strontium hexaferrites having a high level of chromium substitution (SrFe_12−x Cr_x O₁₉, x = 0–6) and investigate their structural, morphological, and magnetic properties.

Methods. The synthesis was carried out using the solid-phase reaction method at a temperature of 1400°C. The impact of chromium substitution for iron on the phase, structure, morphology, and magnetic characteristics was studied using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and vibrating-sample magnetometry.

Results. XRD analysis confirmed the development of single-phase samples having a hexagonal space group P6₃/mmc. An increase in Cr concentration leads to a decrease in unit cell parameters, due to the smaller ionic radius of Cr³⁺. The surface morphology of the samples consists of bulk crystallites a few microns in length. Substitution with Cr results in decreased saturation and remanent magnetization.

Conclusions. Pure samples of Cr-substituted strontium hexaferrite were synthesized. The linear dependence of the investigated structural parameters on the Cr concentration confirms the Cr substitution into the hexaferrite solid solution by Vegard’s law. In addition to structural parameters, magnetic characteristics were obtained for hexaferrite solid solutions. Saturation and remanent magnetization dependencies were shown to significantly decrease with Cr concentration, while coercive force varies in a complex dependence on Cr concentration. The sample with x = 1 has the highest product of coercive force and saturation magnetization, indicating its suitability for permanent magnet application.

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