Mössbauer and Optical Investigations on Sr Doped M-Type BaFe12O19 Hexaferrites Produced via Autocombustion

Ba1−xSrxFe12O19 (x = 0.0, 0.5 and 1.0) hard-magnetic nanohexaferrites prepared by autocombustion were primarily investigated using Mössbauer spectroscopy and optical studies. Morphological examination by electron scanning microscopy revealed that the particles agglomerated into grains with a hexagonal shape. The grain size increases with the amount of Sr content, from ca. 490 nm (x = 0.0) to ca. 700 nm (x = 1.0). Room-temperature Mössbauer spectroscopy showed that the mean hyperfine field increased with the substitution of Ba2+ by Sr2+, consistent with magnetization results. The preferential sites occupied by Fe ions in the hexaferrite structure were determined. Optical studies revealed that all compounds absorb up to ca. 1000 nm, and that the bandgap energy decreases with increasing Sr content.