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 that reduction of iron oxides proceeded at temperatures above 650 °C. The most intensive peaks of α-Fe were observed in XRD patterns of the samples heat treated at 850 and 950 °C. Magnetic property measurements showed that saturation magnetization of the milled sample increased considerably and coercivity decreased by heat treating at 950 °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.