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

Abstract

This research work aims to study the effect of co-doping by Al3+ to increase the electronic charge carrier concentration inversely to Mg2+. Zn0.97Gd0.03O, Zn0.95Gd0.03Mg0.02O, and Zn0.95Gd0.03Al0.02O 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 μB. 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.