Nd–Co substituted strontium hexaferrite powders with enhanced coercivity

Graphical abstract: Display Omitted Highlights: ► Sr{sub 1−x}Nd{sub x}Fe{sub 11−x}Co{sub x}O{sub 19} was prepared by sol–gel auto-combustion method with 0 ≤ x ≤ 0.4. ► Coercivity increases 11% with 0.2 Nd–Co substitution, reaching a value of 68.9 A/m. ► The appearance of two magnetic orderings is noticed in susceptibility measurements. ► This is supported by Curie temperature and susceptibility data. -- Abstract: In this work we report the synthesis of Nd–Co substituted strontium hexaferrites of composition Sr{sub 1−x}Nd{sub x}Fe{sub 11−x}Co{sub x}O{sub 19} by the sol–gel auto-combustion method with further heat treatment. The analysis of the X-ray diffraction spectra shows the M-type hexagonal structure in samples treated at 1100 °C for 2 h. Coercivity increases 11% with 0.2 Nd–Co substitution, reaching a value of 68.9 A/m (5480 Oe) while saturation magnetization is reduced 6% to 91 A m{sup 2}/kg (91 emu/g). The behavior of magnetic susceptibility with an applied field shows two different maxima which are assigned to different magnetic orderings. This assumption is supported by the appearance of two experimental values of Curie temperatures (T{sub C}) for all the prepared samples. Magnetic susceptibility χ and T{sub C} measurements suggest an uneven distribution of the iron vacancies.