Properties of Cr-substituted M-type barium ferrites prepared by nitrate-citrate gel-autocombustion process

The Cr-substituted M-type barium hexaferrites, BaFe12-xCrxO19, with x = 0.0-0.8 have been successfully prepared by nitrate-citrate auto-combustion process using citric acid as a fuel/reductant and nitrates as oxidants. The resulting precursors were calcined at 1100 degrees C for 1 h and followed by sintering at 1200 degrees C for 12h in oxygen atmosphere. The ferrites were systematically investigated by using powder X-ray diffractometer (XRD), magnetic hysteresis recorder, Mossbauer spectrometer, and scanning electron microscope (SEM). The XRD data show the formation of pure magnetoplumbite phase without any other impurity phases. Both a and c lattice parameters calculated by the Rietveld method systematically decrease with increasing Cr content. The effects of Cr3+ ions on the barium ferrites were reported and discussed in detail. The site preference of Cr3+ and magnetic properties of the ferrites have been studied using Mossbauer spectra and hystereses. The results show that the magnetic properties are closely related to the distributions of Cr3+ ions on the five crystallographic sites. The saturation magnetization systematically decreases, however, the coercivity increases with Cr concentration. The magnetization and Mossbauer results indicate that the Cr3+ ions preferentially occupy the 2a, 12k, and 4f(VI) sites. The average size of hexagonal platelets obtained by SEM photographs tends to decrease with respect to Cr content. (c) 2005 Elsevier B.V. All rights reserved.