Structural and magnetic properties of La-doped strontium-hexaferrites ceramics obtained by spark-plasma sintering

• Sr 1 - x La x Fe 12 O 19 (x = 0.1, 0.3, and 0.6) hexaferrite were successfully obtained by spark-plasma sintering (SPS) from as-calcined powders. • Finite element simulation of the SPS process. • Rietveld refinement of the samples obtained under SPS condition and with different La-content. • The Sr 1 - x La x Fe 12 O 19 is dominant phase and the contribution of secondary phases does not reduce the coercivity of the system. • First-order reversal curves (FORC) revealed details of the magnetic behavior of the samples. Polycrystalline samples of Sr 1− x La x Fe 12 O 19 ( x = 0.1, 0.3, and 0.6) hexaferrite were prepared by spark-plasma sintering (SPS) and its structural and magnetic properties have been investigated. The SPS process were performed under vacuum, at 900 °C , and in only 5 min. X-ray powder diffraction patterns showed that before SPS sintering samples are composed by several phases where the SrFe 12 O 19 (SrM) is not higher than 12 % . From Rietveld refinement method, we have found that after SPS process the content of SrM phase increased, in mean, up to 68 % . However, it was found the presence of secondary phase such as α -Fe 2 O 3 and LaFeO 3 ( % ) whose phase content also vary with increasing the La-content. A finite element simulation model were used to study the temperature evolution within the sample during the SPS treatment. Magnetization measurements at room temperature yielded values of saturation magnetization between ~ 43 to ~ 27 emu/g and coercivities, H cB , in the range 3.11 to 2.88 kOe with increasing x . The influence and possible interaction between detected magnetic phases was studied by means of first-order reversal curves (FORCs) measurements. Results indicated that magnetic behavior of the La-doped strontium hexaferrites obtained by SPS technique are analogous a system composed of a broad distribution particles that are exchange-coupled with a certain number of other of neighboring particles. From FORC maps the coercivity profiles of the studied samples were extracted. The asymmetric behavior of these profiles were related to a broad distribution of the particle size and/or the influence of the secondary magnetic phases.