Morphology and Magnetic Coupling in ZnO:Co and ZnO:Ni Co-Doped with Li

C. Perssona,b, O.D. Jayakumarc, C. Sudakard, V. Sudarsanc and A.K. Tyagic aDepartment of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden bDepartment of Physics, University of Oslo, P.O.Box 1048 Blindern, NO-0316 Oslo, Norway cChemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India dDepartment of Physics and Astronomy, Wayne State University, Detroit, MI 48201, USA

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Zn0.95Co0.05O and Zn0.97Ni0.03O nanorods, prepared by a solvothermal method, show intriguing morphology and magnetic properties when co-doped with Li. At low and moderate Li incorporation (below 10 and 3 at.% Li in the Co- and Ni-doped samples, respectively) the rod aspect ratio is increased and room temperature ferromagnetic properties are enhanced, whereas the ferromagnetic coupling in Zn0.97Ni0.03O is decreased for Li concentrations > 3 at.%. First-principles theoretical analyses demonstrate that Li co-doping has primarily two effects in bulk Zn1- xMxO (with M = Co or Ni). First, the Li-on-Zn acceptors increase the local magnetic moment by depopulating the M 3d minority spin-states. The magnetic coupling is Ruderman-Kittel-Kasuya-Yosida-like both without and with Li co-doping. Second, Li-on-Zn prefer to be close to the M atoms to compensate the M-O bonds and to locally depopulate the 3d states, and this will help forming high aspect nanostructures. The observed room temperature ferromagnetism in Li co-doped Zn1- xMxO nanorods can therefore be explained by the better rod morphology in combination with ionizing the magnetic M atoms.

DOI: 10.12693/APhysPolA.119.95 PACS numbers: 71.20.Nr, 71.55.Gs, 75.50.-y