Structural, morphological, magnetic and optical properties of chromium substituted strontium ferrites, SrCrxFe12 − xO19 (x = 0.5, 1.0, 1.5, 2.0 and 2.5) annealed with potassium halides

Chromium substituted strontium ferrites SrCrxFe12 − xO19 (x = 0.5, 1.0, 1.5, 2.0 and 2.5) have been synthesized via sol gel method and the dry gels obtained have been annealed with various inorganic template agents (KCl, KBr and KI). The powder X ray diffraction studies reveal a crystallite size of ~ 40–45 nm. The use of KCl as inorganic template agent leads to an increase in the crystallite size. This may be attributed to the fact that the coordination ability of Cl− is maximum due to its larger charge to size ratio, which promotes crystal growth in one dimension leading to needle-like morphology. On the other hand, KI undergoes sublimation to form I2 which gets entrapped in the strontium ferrite crystal leading to a bubble-like morphology. A systematic change in the lattice constants, a and c, is not observed because the radius of Cr3+ ion (0.63 Å) is similar to that of Fe3+ ion (0.64 Å). The saturation magnetization decreases with increase in the chromium concentration from 43.03 emu/g to 17.40 emu/g due to the substitution of Fe3+ ions by less magnetic Cr3+ ions in 2a and 12k sites of the lattice. The coercivity decreases with increase in the chromium concentration due to decrease in magnetocrystalline anisotropy. In the presence of KCl and KBr, both saturation magnetization and coercivity increase and the saturation magnetization has the maximum value in case of samples annealed with KBr. However, with KI, the values of both saturation magnetization and coercivity decrease sharply which may be due to lower crystallinity due to bubble-like morphology because of the decomposition of KI to I2. The energy band gap for all the ferrite compositions is found to be ~ 2.2 eV and its value increases in the samples annealed with KI.