Effects of Ni doping on structural, magnetic and catalytic properties of copper ferrite

The aim of this work was to obtain information about the influence of small quantities of Ni$²⁺$ ion on thestructural and magnetic properties of the tetragonally distorted of Cu$_1-x$Ni$_x$Fe$_2$O4 series (with x = 0.00, 0.05,0.1, and 0.15 respectively). The tested ferrite system was synthesized by combustion of citrate–nitrate precursors.The synchrotron X-ray diffraction measurements determined the phase transition temperatures (tetragonal →cubic) of all samples. The change of structures under the influence of temperature shows a phase transition in therange of 390 – 400 ◦C for x = 0.00, 330 – 370 ◦C for x = 0.05, 210 – 330 ◦C for x = 0.1 and 140 – 210 ◦C for x= 0.15, respectively. The initial phase transition temperature decreases linearly with the decreasing c/a ratio ofthe crystallographic lattice parameters for the Cu$_1-x$Ni$_x$Fe$_2$O$_4$ oxides. Hysteresis measurements were made todetermine the saturation magnetization (M$_S$) and coercive field (μ$_0$H$_c$) of the samples. The values of magneticmoments at room temperature determined from magnetization measurements are very similar to those obtainedfrom theoretical x-ray diffraction calculations. Magnetic moment values per formula unit are estimated to rangefrom 1.16 μB to 1.5 μB. It was found that the catalytic activity of N$_2$O decomposition of samples increases withincreasing nickel content.