Structural and magnetic properties of ball milled copper ferrite
Journal of Applied Physics
The structural and magnetic evolution in copper ferrite (CuFe 2 O 4 ͒ caused by high-energy ball milling are investigated by x-ray diffraction, Mössbauer spectroscopy, and magnetization measurements. Initially, the milling process reduces the average grain size of CuFe 2 O 4 to about 6 nm and induces cation redistribution between A and B sites. These nanometer-sized particles show superparamagnetic relaxation effects at room temperature. It is found that the magnetization is not saturated even
... not saturated even with an applied field of 9 T, possibly as the result of spin canting in the partially inverted CuFe 2 O 4 . The canted spin configuration is also suggested by the observed reduction in magnetization of particles in the blocked state. Upon increasing the milling time, nanometer-sized CuFe 2 O 4 particles decompose, forming ␣-Fe 2 O 3 and other phases, causing a further decrease of magnetization. After a milling time of 98 h, ␣-Fe 2 O 3 is reduced to Fe 3 O 4 , and magnetization increases accordingly to the higher saturation magnetization value of magnetite. Three sequential processes during high-energy ball milling are established: ͑a͒ the synthesis of partially inverted CuFe 2 O 4 particles with a noncollinear spin structure, ͑b͒ the decomposition of the starting CuFe 2 O 4 onto several related Fe-Cu-O phases, and ͑c͒ the reduction of ␣-Fe 2 O 3 to Fe 3 O 4 .