Characterization of manganese and titanium co-substituted M-type hexaferrites

: A series of six samples of the M-type ferrite BaFe 12– x – y Ti x Mn y O 19 were synthesized from sodium carbonate flux in order to obtain a consistent set of data on the substitution mechanisms, a prominent material class for example used as permanent magnets and microwave absorbers. The study aims to elucidate the interrelations of synthesis technique, degree of substitution, valence states of the transition metal constituents and magnetic properties. The samples were single phase and both lattice parameters a and c increase with increasing degree of substitution. X-ray absorption spectroscopy measurements gave no evidence for the presence of Mn 4+ , Ti 3+ , nor significant amounts of Fe 2+ . This leads to the conclusion that the charge balance in the bulk material is achieved by Mn 2+ /Ti 4+ , while excess manganese substitutes Fe 3+ in an isovalent manner. X-ray photoelectron spectroscopy measurements indicate a different situation on the crystal surface, with additionally Fe 2+ and Mn 4+ present in non-negligible amounts. Wavelength dispersive X-ray analysis confirmed that the incorporation of titanium and manganese does generally not occur to the same degree, as the maximum degree of substitution found for titanium was x = 1 and for manganese y = 3. According to the volumes of coordination polyhedra the tetrahedra showed a clear increase in volume, which confirms the assumption that the larger Mn 2+ substitutes Fe 3+ at this site. The octahedra at site 2 a showed a decrease in volume with increasing degree of substitution, which indicates that Ti 4+ is predominantly located there. Saturation magnetization, coercivity and remanence were studied as function of substitution at 27 °C and −270 °C. The Curie temperature decreases monotonous with increasing degree of substitution. This comprehensive set of data obtained from high-quality samples synthesized under identical conditions enlightens the complex situation in this particular co-substituted ferrite system and allows conclusions and predictions for similar systems.