STRUCTURAL AND MAGNETIC-PROPERTIES OF BALL-MILLED COPPER FERRITE

The structural and magnetic evolution in copper ferrite (CuFe2O4) caus ed by high-energy ball milling are investigated by x-ray diffraction, Mossbauer spectroscopy, and magnetization measurements. Initially, the milling process reduces the average grain size of CuFe2O4 to about 6 nm and induces cation redistribution between A and B sites. These nano meter-sized particles show superparamagnetic relaxation effects at roo m temperature. It is found that the magnetization is not saturated eve n with an applied field of 9 T, possibly as the result of spin canting in the partially inverted CuFe2O4. The canted spin configuration is a lso suggested by the observed reduction in magnetization of particles in the blocked state. Upon increasing the milling time, nanometer-size d CuFe2O4 particles decompose, forming alpha-Fe2O3 and other phases, c ausing a further decrease of magnetization. After a milling time of 98 h, alpha-Fe2O3 is reduced to Fe3O4, and magnetization increases accor dingly to the higher saturation magnetization value of magnetite. Thre e sequential processes during high-energy ball milling are established : (a) the synthesis of partially inverted CuFe2O4 particles with a non collinear spin structure, (b) the decomposition of the starting CuFe2O 4 onto several related Fe-Cu-O phases, and (c) the reduction of alpha- Fe2O3 to Fe3O4. (C) 1998 American Institute of Physics. [S0021-8979(98 )02514-6].