Structural and magnetic properties of ball milled copper ferrite

The structural and magnetic evolution in copper ferrite $({\mathrm{CuFe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}\mathrm{)}$ 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 ${\mathrm{CuFe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}$ 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 with an applied field of 9 T, possibly as the result of spin canting in the partially inverted ${\mathrm{CuFe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}.$ 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 ${\mathrm{CuFe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}$ particles decompose, forming $\mathrm{\alpha -}{\mathrm{Fe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ and other phases, causing a further decrease of magnetization. After a milling time of 98 h, $\mathrm{\alpha -}{\mathrm{Fe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ is reduced to ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{4}}\mathrm{,}$ and magnetization increases accordingly to the higher saturation magnetization value of magnetite. Three sequential processes during high-energy ball milling are established: (a) the synthesis of partially inverted ${\mathrm{CuFe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}$ particles with a noncollinear spin structure, (b) the decomposition of the starting ${\mathrm{CuFe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}$ onto several related Fe–Cu–O phases, and (c) the reduction of $\mathrm{\alpha -}{\mathrm{Fe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ to ${\mathrm{Fe}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{4}}\mathrm{.}$