Effect of cobalt and aluminum doping on the structural and magnetic properties of zinc oxide nanoparticles

A systematic study of the substitution effect of Co and Al on ZnO nanoparticles was carried out by x-ray diffraction (XRD) and transmission electron microscopy and using a superconducting quantum interference device magnetometer to study their structural, morphological, and magnetic properties. Zn1-xMxO (M = Co, Al) at different doping concentrations was prepared using a hydrothermal technique. The XRD results with structural Rietveld refinement reveal that the major phase of all samples had a hexagonal wurtzite crystal structure with a P6(3)mc space group. Hysteresis loops with no magnetic saturation at high fields were analyzed at 2 K in all samples. Zero magnetic remanence and zero coercivity were also examined. The results demonstrated that the magnetic ground state at 2 K in all samples was magnetism with the coexistence of antiferromagnetic, ferromagnetic, and superparamagnetic phases. This behavior persisted at 100 and 300 K in the Al-doped sample, while Co-doped ones exhibited a paramagnetic state only. The role of non-magnetic doping, which leads to the appearance of magnetism in ZnO nanoparticles persisting at high temperatures, is discussed herein.