Structural and magneto-optical investigations of citrate sol–gel derived barium hexaferrite nanocrystalline powder

Abstract

Magneto-optical measurements enable the identification of Fe2+ and Fe3+ in the R and S blocks of BaFe12O19 M-hexaferrite powder obtained by sol-gel processing, followed by thermal annealing at 900 C for 3 hours. The ferromagnetic phase is evidenced by the spin-majority configuration (Fe3+) due to their unpaired electrons between d-d orbitals, while the Fe2+ in the low spin possesses diamagnetic behavior strongly dependent on the surrounded crystal field. Additionally, the irradiation with gamma rays changes the ratio between Fe2+/Fe3+, mainly on the surface of BaFe12O19 nanocrystals. These changes were confirmed by X-ray Photoelectron Spectroscopy measurements, in which the concentration of Fe2+ increased from 69% to 82%, while the one of Fe3+ decreased from 31% to 18%. he thermoluminescent measurements reveal the same changes of Fe3+ in Fe2+ by electron capturing during irradiation, which is released as a red emission after recombination processes. The changes are explained by the increasing of some Fe-O bonds along the c-axis, mainly due to breaking a part of these bonds. The X-ray analysis confirms the changing of the parameters for the BaFe12O19 hexagonal structure.