New Dy-substituted Ba hexaferrites with high coercivity

Single-phase hexaferrite compounds were obtained in a novel series of Dy-substituted Ba hexaferrites with nominal formula (Ba_1-x,Dy _x)O · 5.25 Fe₂O₃ (x =0-0.30). The samples were prepared by the chemical coprecipitation method from nitrate precursors and calcination at T = 900-1200°C for 2 h. Analysis of XRD powder patterns shows that all samples are M-type hexagonal ferrites, with Fe ₂O₃ only impurities, indicating the incorporation of Dy in the hexaferrite structure. Single-phase compounds are obtained at T = 900-1100°C, for a x range up to 0.05-0.15. Fe₂O₃ is found from traces up to 20%, for higher temperature and x values. Magnetization at 1.8 T decreases with x, but coercivity remains high at values close to 400-440 kA/m in most cases, regardless of the x value and impurity content. The high coercivity values related to the presence of Dy may be attributed to microstructural effects such as grain growth inhibition or to variation of the magnetocrystalline anisotropy.