Structural, dielectric, and magneto-optical properties of Cu2+-Er3+ substituted nanocrystalline strontium hexaferrite

Nanocrystalline Cu²⁺-Er³⁺ substituted M-type strontium hexaferrites with chemical composition Sr_1-xCu_xFe_12-yEr_yO₁₉ (x = 0.0, 0.1, 0.2, and y = 0.0, 0.4, 0.5) was synthesized using sol-gel autocombustion method, pre-sintered at 400 °C for 3 h and sintered at 950 °C for 6 h. XRD patterns shows that the sample exhibit pure crystalline structure with the absence of magnetite (α-Fe₂O₃) and other secondary phases. The idea of the formation of M-type hexagonal ferrite was given by the presence of two prominent peaks at 454 and 591 cm^-1 in the spectra of FTIR. FESEM micrographs show agglomerated crystallites as a result of magnetic interaction between the crystallites. The band gap calculated from UV-vis NIR spectroscopy increase with Cu²⁺-Er³⁺ with substitution. The dielectric properties were discussed using Koop's phenomenological and Maxwell-Wagner model. The Er³⁺ ions causes spin canting effect, magnetic dilution and the collapsed of the magnetic collinearity thereby resulting in decrease magnetization. The Cu²⁺ ions influence the magnetocrystalline anisotropy in a negative manner thereby leading to reduced coercivity.