Structural,microwave permittivity,and complex impedance studies of cation (Cr,Bi, Al,In) substituted SrNi-X hexagonal nano-sized ferrites

Sr₂Ni₂T_xFe_28-xO₄₆ (T = Cr³⁺, Bi³⁺, Al³⁺, In³⁺; x = 0.25) hexa-ferrites were fabricated via the sol-gel route. The phase temperature, which was obtained using thermo-gravimetric analysis (TGA), reveals that the X-type hexagonal phase of these materials is highly stable above 1200 °C. The phase formation was confirmed using X-ray diffraction (XRD) patterns. The variation in lattice strain shows the significant effect of substituted cations on the structure of the materials. The crystallite size of these materials was found in the range of 18–19 nm. The increase in dielectric constant, as well as with moderate loss, was observed in all substituted samples between 0.001 GHz and 1 GHz. The large values of dielectric constant were observed for Al³⁺ and In³⁺ substituted materials at higher frequency. The values of slope (n) reveal that all the materials exhibit frequency dependent ac conductivity. The Cole-Cole plots show the single semicircle for all samples. These semicircles of the Cole-Cole plots indicate that resistance inside the material is due to grains and grain boundaries. The both grain and grain boundaries resistance inside the material may cause large values of dielectric constant as well as the losses in the material. The large values of dielectric constant and impedance with moderate dielectric losses of these materials reflect their significant role in the fabrication of electronic devices as a radiation/microwave absorber or high frequency equipment components. Magnetic analysis shows the large values of magnetization and coercivity for Al³⁺ and In³⁺ substituted samples, which reflect that these materials might be beneficial for the absorption of electromagnetic radiation, formation of multilayer chip inductors and recording/storage purpose.