MAGNETIC-PROPERTIES OF COPPER-MAGNETITE NANOCOMPOSITES PREPARED BY BALL-MILLING

Small particles of Fe3O4, embedded in a Cu matrix, have been prepared both by direct milling of a mixture of Cu and Fe3O4 and by reaction milling of CuO and Fe. It is shown that the most significant changes in phase composition, magnetization, coercivity, remanence, and switching field distribution take place during the first 2 h of milling. Both processes provide small (about 25 nm) semihard magnetite particles after 1 h, with H(c) up to 350 Oe and squareness of 0.3. Prolonged milling causes partial oxidation of magnetite to alpha-Fe2O3 and the presence of superparamagnetic magnetite particles, both reducing the magnetization of the composites. Conclusions based on magnetic measurements about the details of the technological process and microstructural changes are in very good agreement with results of x-ray diffraction measurements.