Enhancement in the dielectric and magnetic properties of Ni2+–Cu2+ co-doped BaFe11Cu1−xNixO19 hexaferrites (0.0 ≤ x ≤ 1.0)

Abstract

Herein, Ni²⁺–Cu²⁺ co-doped barium hexaferrites (BaFe₁₁Cu_1−xNi_xO₁₉, 0.0 ≤ x≤ 1.0 with an interval of 0.25) were successfully synthesized using a co-precipitation method. The formation of a magnetoplumbite structure with the P6₃/mmc space group was confirmed by Rietveld refinement of the obtained X-ray diffraction patterns. Microstructural investigations revealed grains in the shape of hexagonal plates, while co-doping resulted in a variation in the grain sizes of the prepared samples. X-ray photoelectron spectroscopy was performed to determine the valence state of iron in the prepared hexaferrites. Impedance spectroscopy analysis revealed that dielectric permittivity initially decreased with an increase in the co-dopant content up to x = 0.5 and then increased by two orders of magnitude for x = 1.0. Alternatively, resistive properties showed microstructural resistance values in the range 10⁵–10⁸ Ω, with the highest value obtained for the sample with x = 0.5. Furthermore, magnetic measurements indicated that all the prepared samples exhibited ferrimagnetic behaviour. Saturation magnetization and magnetic anisotropy values were found to be the highest for the sample with x = 1.0, which also had the lowest coercivity among the prepared samples. Herein, the observed variations in the obtained results can be explained by the variations in grain sizes and the Fe²⁺/Fe³⁺ ratio associated with the preferential occupation of co-dopants at octahedral sites. Based on our findings, the BaFe₁₁Ni₁O₁₉ (x = 1.0) composition appears to be the most promising choice as a microwave absorption material among the prepared samples owing to the coexistence of high dielectric permittivity (>10³ at 10⁷ Hz) and saturation magnetization (73 emu g⁻¹).