Effect of nickel doping concentration on structural and magnetic properties of ultrafine diluted magnetic semiconductor ZnO nanoparticles

The ZnO:Ni2+ nanoparticles of mean size 2–12 nm were synthesized at room temperature by the simple co-precipitation method. The crystallite structure, morphology and size were determined by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The wurtzite structure of ZnO gradually degrades with the increasing Ni doping concentration and an additional NiO-associated diffraction peak was observed above 15% of Ni2+ doping. The change in magnetic behavior of the nanoparticles of ZnO with varying Ni2+ doping concentration was investigated using a vibrating sample magnetometer (VSM). Initially, these nanoparticles showed strong ferromagnetic behavior, however, at higher doping percentage of Ni2+, the ferromagnetic behavior was suppressed and paramagnetic nature was observed. The enhanced antiferromagnetic interaction between neighboring Ni–Ni ions suppressed the ferromagnetism at higher doping concentrations of Ni2+.