Nanocomposite formation in the Fe3O4-Zn system by reaction milling

Abstract

Magnetic nanocomposites of small iron particles embedded in nonmagnetic zinc oxide matrix have been prepared by ball milling, with an in situ displacement reaction between a metal oxide (Fe₃O₄) and a more reactive metal (Zn). The phase composition of the samples has been analyzed by x‐ray diffraction. Metallic zinc disappears during the first 100 min of milling and the magnetization decreases to almost zero, indicating the formation of a nonmagnetic intermediate iron‐zinc oxide phase. This intermediate phase decomposes into iron and ZnO upon further milling. The change in magnetic properties also reflects the decreasing size of the iron particles. The final particle size is about 9 nm, as estimated from x‐ray diffraction linewidth measurements. The final product of the process is a semihard magnetic material with a room‐temperature saturation magnetization of 40 emu/g and coercivity of 400 Oe. A significant fraction of the final Fe particles is superparamagnetic.