Multiferroic Ba1.6Sr1.4Co2Fe24O41 with a Z-type hexagonal structure was obtained through the proteic sol-gel process with a single-phase, combined with thermal treatment at 1200 °C for 2 h. XRD analysis revealed the formation of a single phase, with preferential orientation in the case of a sample in pellet form. Magnetometry measurements revealed a low coercive field characteristic of Z-type hexaferrite, plus an electrical resistivity of approximately 2 × 109 Ω.cm that was considerably higher than expected.

A new W-type hexaferrite (Sr0.85Ce0.15Co2Fe16O27-δ) was synthesized through proteic sol-gel using coconut water as a solvent for the precursor salts. Structural analysis was carried out using an X-ray diffractometer (XRD). The XRD results showed that the resulting ceramic exhibited preferential orientations along the crystal planes in addition to lattice displacements. The magnetic properties evaluated using a vibrating sample magnetometer indicated a high saturation magnetization value and low coercive field and remnant magnetization values. The Curie temperature determined through differential scanning calorimetry was 473 oC. The electric resistivity value determined through complex impedance was similar to those already reported in the literature, thus promising the use of this hexaferrite in electronic and microwave device applications.

Sr1-xGdxCo2Fe16O27-δ, (x = 0.05–0.20) was prepared via the proteic sol-gel process. Single-phase W-type hexaferrite doped with gadolinium was synthesized. The ferrite shows ferrimagnetic behavior with high saturation magnetization, low coercive field, low remnant magnetization, and a resistivity greater than 107 Ω·cm. The substitution of Sr2+ for Gd3+ improved the magnetoelectric properties of the ferrite owing to the increase in the concentration of Fe2+ and improvement of electron conduction.

Samples of CayFe12-yO19 (0 ≤ y ≤ 1.0) were prepared by a proteic sol–gel process with hematite phase and clusters of M-type calcium hexaferrite. Impedance analysis showed that the resistivity increased with calcium concentration in the 0.0 < y ≤ 0.2 range, but decreased for y > 0.2. The saturation of the electrical resistivity occurred at 7.5 × 106 Ω·cm for Ca0.9Fe11.1O19. The plot of magnetization as a function of the magnetic field showed high values of saturation magnetization (40 emu/g) with low remanence (6.7 emu/g) and coercive field (320 Oe).