Mossbauer and magnetic study of nanocrystalline strontium hexaferrite prepared by an ionic coordination reaction technique

Hard-magnetic nanocrystalline strontium hexaferrites SrFe12O19 were synthesized using an ionic coordination reaction technique. In this sample preparation technique the biopolymer chitosan was used as a nanoreactor. The obtained precursor powders were calcined at temperatures in the range 600-900 degrees C. The samples were analyzed by X-ray diffraction, transmission electron microscopy, Mossbauer spectroscopy and vibrating sample magnetometry. A complementary study of X-ray Rietveld refinement and Mossbauer spectroscopy shown that the hexaferrite phase formation is accompanied by formation of maghemite and hematite as intermediate phases. It was found that hexaferrite is present in the samples calcined at and above 600 degrees C but it is fully developed at 900 degrees C. For this sample the average particle size was found to be 41.6 nm. Magnetization measurements yielded squared hysteresis loops with a magnetization ratio (M-r/M-s) of 0.58 and a coercive field of 6.48 kOe. The overall results indicated that the particles in these samples are in the single domain regime and that the magnetization reversal in these particles is mainly due to coherent rotation. (C) 2013 Elsevier B.V. All rights reserved.