Magneto-optical properties of SrxBixLaxFe12-2xO19 (0.0 <= x <= 0.5) hexaferrites by sol-gel auto-combustion technique

SrxBixLaxFe12-2xO19 (0.0 <= x <= 0.5) hexaferrites were synthesized by sol-gel auto combustion technique. The influence of Bi and La substitutions on structural, magnetic and optical properties were investigated by X-ray diffraction (XRD), Furrier transformed infrared (FT-IR), Vibrating sample magnetometer (VSM) and Percent diffuse reflectance spectroscopy (DR %). XRD analysis confirmed the single phase formation for all the samples, the purity of the products was also confirmed by FT-IR. The specific magnetization (sigma-H) curves revealed the ferromagnetic nature of the samples. The extrapolated specific saturation magnetization (sigma(s)) decreases from 63.45 emu/g to 49.84 emu/g with increasing Bi, La substitutions. Similar decrement is observed from 32.6 emu/g to 25.8 emu/g at remnant magnetization (sigma(r)). The average crystallite size varies in a range of (43.28-51.40) nm. The coercive fields are between 4682 and 5315 Oe. Magnetic anisotropy was assigned as uniaxial and calculated effective anisotropy constants (K-eff) are between 5.57x10(5) Ergs/g and 4.03x10(5) Ergs/g. The observed high magnitudes of intrinsic coercivity (H-ci) above 16,000 Oe confirm hard magnetic nature of the samples. The Tauc plots were used to extrapolate the direct optical energy band gap (E-g) of hexaferrites. The E-g values decreased from 1.81 to 1.68 eV with increasing Bi, La contents.