The effect of heat treatment and re-calcination on magnetic properties of BaFe12O19/Fe3O4 nano-composite

In this study a mixture of barium hexaferrite (BaFe12O19) and graphite was subjected to intensive milling in a planetary ball mill in order to synthesize BaFe12O19/Fe3O4 magnetic nano-composite. The effects of milling time and post-synthesis heat treatment on the powder characteristics were investigated using XRD, VSM and HRTEM techniques. XRD results showed that barium hexaferrite partially reduced during high-energy ball milling and nano-composite of BaFe12O19/Fe3O4 was obtained after 15 h milling of the initial mixture. Analysis of the 40 h milled and then heat-treated samples revealed than reduction of iron oxides proceeded at temperatures above 650 degrees C. The most intensive peaks of alpha-Fe were observed in XRD patterns of the samples heat treated at 850 and 950 degrees C. Magnetic property measurements showed that saturation magnetization of the milled sample increased considerably and coercivity decreased by heat treating at 950 degrees C. Re-calcination of the aforementioned sample resulted in an increase in coercivity value to 3444.62 Oe. HRTEM image showed nano-crystalline Fe3O4 in the structure of 40 h milled sample. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.