NANOCOMPOSITE FORMATION IN THE FE3O4-ZN SYSTEM BY REACTION MILLING

Magnetic nanocomposites of small iron particles embedded in nonmagneti c zinc oxide matrix have been prepared by ball milling, with an in sit u displacement reaction between a metal oxide (Fe3O4) and a more react ive metal (Zn). The phase composition of the samples has been analyzed by x-ray diffraction. Metallic zinc disappears during the first 100 m in of milling and the magnetization decreases to almost zero, indicati ng the formation of a nonmagnetic intermediate iron-zinc oxide phase. This intermediate phase decomposes into iron and ZnO upon further mill ing. The change in magnetic properties also reflects the decreasing si ze of the iron particles. The final particle size is about 9 nm, as es timated from x-ray diff-faction linewidth measurements. The final prod uct of the process is a semihard magnetic material with a room-tempera ture saturation magnetization of 40 emu/g and coercivity of 400 Oe. A significant fraction of the final. Fe particles is superparamagnetic.