Effects of Cu dilution in NiO on the magnetic properties of NiFe2O4/Ni1−xCuxO nanocomposites

A granular system composed of ferromagnetic NiFe2O4 nanoparticles embedded in the Cu diluted NiO matrix has been synthesized by the chemical concentration precipitation method. Phase composition analysis shows that Cu ions have been successfully incorporated into NiO matrix substituting for Ni ions. The magnetic properties of all the bulk samples were investigated by measuring their magnetization as a function of temperature and magnetic field. The field-cooling hysteresis loop shift was observed after cooling the nanocomposites. With the increase of the Cu dilution ratio, the saturation magnetization first increases, and then decreases after reaching a maximum. The exchange bias field gradually decreases with the Cu dilution ratio, reaching a plateau when x ≥ 0.05. These results are tentatively interpretated by the misalignment of magnetic moments between the ferromagnetic and the antiferromagnetic spins. The decrease of the coupling area between the ferromagnetic phase and the antiferromagnetic phase at the interface is another possible reason.