Magnetic property enhancement and characterization of nano-structured barium ferrite by mechano-thermal treatment

In this research a mixture of barium ferrite and graphite powders was milled in a planetary ball mill and then heat treated in vacuum to produce BaFe12O19/Fe3O4 and Fe/Fe3O4 magnetic nano-composites. The effects of milling time and heat treatment temperature on the characteristics of powder mixture were investigated by X-ray diffraction analysis, vibrating sample magnetometer, transmission electron microscopy and Mössbauer spectroscopy. Phase analysis results showed that Fe2O3 in barium ferrite partially reduced to Fe3O4 during milling; hence, the reduced phase and remaining barium ferrite formed a nano-composite of BaFe12O19/Fe3O4 after 20 h of milling. Heat treatment of the 40 h milled samples at 750–900 °C resulted in formation of Fe containing nano-composite. Magnetic measurements indicated that the coercivity of 267.92 Oe for 40 h milled sample decreased to 22.57 Oe by heat treatment at 900 °C, while its saturation magnetization increased from 31.56 to 169.43 emu/g due to the formation of Fe nano-crystallites.

► Barium hexaferrite and graphite were treated mechano-thermally.
► After 20 h milling, a nano-composite of BaFe12O19/Fe3O4 formed.
► Heat treatment of milled sample resulted in formation of Fe/Fe3O4 composite.
► Increasing heat treatment temperature results in higher saturation magnetization.
► The milled and heat treated samples were nano-crystalline.