Sr1-xLaxFe12O19 (0.0≤x≤0.5) hexaferrites: Synthesis, characterizations, hyperfine interactions and magneto-optical properties

A simple sol-gel auto combustion process was used to synthesize La3+ substituted M-type strontium hexaferrite, Sr1-xLaxFe12-xO19 (0.0≤x≤ 0.5). Structural, magnetic, and optical behavior as a function of La3+ substitutions were investigated by Fourier transformed infrared spectroscopy (FT-IR). X-ray powder diffraction (XRD). Scanning electron microscopy (SEM), Mössbauer spectroscopy, vibrating sample magnetometer (VSM), and Diffuse reflectance spectroscopy (DRS). XRD data showed single phase magnetoplumbite structure and Rietveld analysis confirmed P63/mmc space group for all the series. The average crystallite size was found to be in the range of 43.2–48.4 nm. The variation in line width, isomer shift, quadrupole splitting, relative area and hyperfine magnetic field values have been determined from 57Fe Mössbauer spectroscopy data. The fittings accounted for the Fe2+/Fe3+ charge compensation mechanism at the 2a site due to replacement of Sr2+ by La3+. The saturation magnetization (σs) decreases from 57,21 to 63,23 emu/g and remnant magnetization (σr) decreases from 35.6 emu/g to 28.7 emu/g with increasing La substitution. The decrement is sharper at coercive field (Hc) from maximum value of 5325 to minimum 1825 Oe. Demagnetizing factor (N) is 3 times more for the x=0.3, 0.4, and 0.5. However all samples exhibit ferromagnetic behavior at room temperature. Magnetic anisotropy of Hexaferrites was detected as uniaxial and effective anisotropy constants (Keff) were between 5.93×105 and 4.76×105 Ergs/g. The high magnitudes of anisotropy fields (Ha) in the range of 13863–15574 Oe reveal that all hexaferrites are magnetic hard materials. Tauc plots were applied to extrapolate the direct optical energy band gap (Eg) of hexaferrites. The Eg values decreased from 1.83 to 1.34 eV with increasing La content.