Effect of Al doping on the cation distribution in copper ferrite nanoparticles and their structural and magnetic properties

Nanocrystalline CuFe2−xAlxO4 (0.0 ≤ x ≤ 1.0) was synthesized by using the sol-gel method and its structural and magnetic properties were investigated. The crystallite size was observed to decrease from 20 to 6 nm with increasing Al content. The lattice parameters were observed to decrease with increasing Al content. The cation distribution from X-ray intensity calculations revealed that Cu2+ preferably occupied octahedral [B] sites. Al3+ ions replaced the Fe3+ ions in the tetrahedral (A) and the octahedral [B] sites. As a result the Fe3+ concentration at (A) and [B] sites decreases, leading to a suppression of the long range magnetic ordering. Magnetic hysteresis loops were measured at room temperature with a maximum applied magnetic field of ≈1 T. As the Al3+ content increases, the measured magnetic hysteresis curves become more and more narrow, and the saturation magnetization and the remanent magnetization both decrease. The reduction of magnetization with increasing of aluminum content is caused by non-magnetic Al3+ ions and weakened interaction between sublattices. The reduction in the magnetization compared to the bulk may originate from the smallness of particles. This is also accompanied by a coercive field reduction.