Optimization of the structural, optical, and magnetic properties of sol-gel derived La3+ substituted nanostructured barium hexaferrites

The M-type barium hexaferrites have been considered an impeding material for their use as microwave absorbers and storage devices. In present investigation, the La3+ substituted M-type BaFe12-xLaxO19, (where x = 0, 0.2, 0.4, 0.6, 0.8 and 1) was prepared via a facile sol-gel process at 850 degrees C for 3 h. XRD confirmed the hexagonal crystal structure of La3+ substituted BaFe12O19 belonging to P63/mmc space group with the crystallite size in the range of 23.08-39.59 nm, which decreased with the increase in La3+ content. The Rietveld refinements displayed better goodness of fit (chi (2)), which was observed between 1.20-1.90 for proper peak fitting. The W-H plot indicated the decrease in lattice strain (0.21 x 10(-3)-2.14 x 10(-3)) with the increase in La3+ contents. The SEM imaging revealed the agglomerations and estimated the average grain size in the range of 0.42-3.69 mu m. FTIR spectroscopy confirmed the bands in the range of 432-622 cm(-1), which represents stretching and bending vibrations of metal oxide bonds. The tetrahedral site exhibited a higher force constant and lower bond length than the octahedral site in M-type barium hexaferrite. The photoluminescence spectroscopy demonstrated that a prominent peak of La3+ substituted BaFe12O19 near 481 nm, which falls under the visible range with strong blue emission and indicates the radiative defects present in the crystal. At room temperature, the magnetic measurements indicate that the coercivity (H-c) increased, but the saturation magnetization (M-s) and the retentivity (M-r) decreased with the increase in La3+ substitutions. The anisotropy constant (K) and Bohr magnetron number (n(B)) were also evaluated between 0.932 x 10(6)-1.109 x 10(6) erg cm(-3) and 10.28-11.68 mu B, respectively. Hence, the unique photoluminescence and magnetic properties may be responsible for its application in the electronic industry, telecommunication, microwave engineering and storage devices etc.