Room temperature ferromagnetism in Co and Ni co-doped ZnO particles: validation through density functional theory

In this work, magnetism was developed in diamagnetic ZnO through co-doping of both nickel and cobalt with composition CoxNi0.1-xZn0.9O (0 <= x <= 0.1). A systematic investigation was conducted to examine the impact of co-doping in ZnO on its microstructural, morphological, and magnetic properties. All the samples exhibited hexagonal wurtzite structure and the crystallite size increases with Co and Ni paired-doped ZnO particles. The structure exhibited a uniform distribution of spherical grains, which were consistent in shape. The elemental color-mapping and EDX analysis provide conclusive evidence of Zn, O, Ni and Co elements. Raman spectra detect the distinctive band of the wurtzite crystal structure, as well as the combined vibration modes of Ni and Co in the doped samples. The vibrating sample magnetometer studies confirmed the transition of ZnO from diamagnetic to ferromagnetic, as a result of different doping concentrations in the studied samples. The dynamic magnetization measurements were investigated by ferromagnetic resonance (FMR) spectroscopy. Various parameters like magnetization, gyromagnetic ratio, Gilbert damping, extrinsic linewidth was derived from field-sweep FMR data. The structural and magnetic results were further validated theoretically by first-principles density functional theory (DFT) calculations. DFT analysis show that localised spin moments from 3d electrons of Co2+ and Ni2+ ions are principally responsible for the stable long-range magnetic ordering in co-doped ZnO particles. Hence, the development of room temperature ferromagnetism in transparent ZnO can have immense applications in spintronics based quantum computing, and phase-change magnetic memory.