Enhancing the saturation magnetisation in Ni doped ZnO thin films by TOPO functionalization

The saturation magnetization in Ni doped ZnO thin films have been triggered by altering the electronic configuration of ZnO by surface functionalization with Trioctail Phosphine Oxide (TOPO). Initially, Ni doped (3, 5 and 7 mol %) ZnO thin films have been grown by RF magnetron sputtering and the same were functionalized with Trioctylphosphine oxide (TOPO) later by spin coating. The XRD analysis confirms the hexagonal wurtzite structure of grown films. It has been found that lower grain size for both unfunctionalized and functionalized 5 mol% Ni doped ZnO films. PL emission at around 530 nm reveals the presence of oxygen vacancies which is actually cause for origin of ferromagnetism. The saturation magnetization values of 5.70 emu/cm(3), 10.14 emu/cm(3) and 8.51 emu/cm(3) obtained for Ni doped ZnO films from VSM have been enhanced to 7.81 emu/cm(3), 11.51 emu/cm(3) and 9.61 emu/cm(3) upon TOPO functionalization. The high saturation magnetization in 5 mol% Ni doped ZnO film is attributed to lower crystallite size (high grain boundaries) and higher oxygen vacancies. The Zn-P bond observed in the XPS spectrum reveals the formation of the surface layer between Zn and P atom which is responsible for the enhancement of saturation magnetization. The presence of peak at 1146 cm(-1) in Raman spectra also confirms the presence of functionalized element, P from TOPO. The simple mechanism based on the bound magnetic poloran and charge distribution has been proposed to explain the origin of room temperature ferromagnetism.