Hydrogen induced changes of optical and magnetic properties of nanocrystalline Zn0.95Gd0.03M0.02O (M=Al,Mg): Experimental and DFT studies

This research work aims to study the effect of co-doping by Al³⁺ to increase the electronic charge carrier concentration inversely to Mg²⁺. Zn_0.97Gd_0.03O, Zn_0.95Gd_0.03Mg_0.02O, and Zn_0.95Gd_0.03Al_0.02O nanopowders were synthesised by simultaneous thermal co-decomposition of a mixture of cadmium and metal complexes, followed by hydrogenation at 350 and 600 °C. This study aimed at establishing the preparation conditions including hydrogenation that were essential for the creation of room temperature ferromagnetic order starting from the paramagnetic Gd-doped ZnO by using structural and electronic consequences of codoping with ions of Al or Mg. X-ray diffraction analysis confirms total doping of (Gd, Mg and Al) impurities into ZnO host lattice as well as the absence of secondary compounds/oxides in the synthesised solid solutions. The reflectance has been found to be significantly affected upon co-doping and hydrogenation, while the energy band gap decreases slightly; i.e. Eg = 3.23–3.00 eV. Magnetic measurements reveal that all the as-synthesised doped ZnO powders gained paramagnetic behaviour defeating the diamagnetic characteristic of ZnO, due to the presence of Gd ions with an effective magnetic moment in the range 8.04–7.12 μ_B. The hydrogenation in the present work conditions did not change the paramagnetic behaviour except for ZnO:Gd:Al-H, showing a partial a magnetic order overlapping with paramagnetic component, resulting in a coercivity of 170.2 Oe, remanence of 0.550 memu/g, and saturation magnetization of 2.14 memu/g. Therefore, the conditions including hydrogenation that were necessary to create FM ordering were determined. First-principles calculations indicate that the Gd doped ZnO systems own large spin polarized effect due to the interaction between Gd-f and O-p electrons. The Mg and Al dopants can modulate the values of magnetic moments.