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In this work, we present the role of vanadium ions (V +5  and V +3 ), oxygen vacancies (V O ), and interstitial zinc (Zn i ) to the contribution of specific magnetization for a mixture of ZnO-V 2 O 5  nanoparticles (NPs). Samples were obtained by mechanical milling of dry powders and ethanol-assisted milling for 1 h with a fixed atomic ratio V/Zn?=?5% at. For comparison, pure ZnO samples were also prepared. All samples exhibit a room temperature magnetization ranging from 1.18?×?10 −3  to 3.5?×?10 −3  emu/gr. Pure ZnO powders (1.34?×?10 −3  emu/gr) milled with ethanol exhibit slight increase in magnetization attributed to formation of Zn i , while dry milled ZnO powders exhibit a decrease of magnetization due to a reduction of V O  concentration. For the ZnO-V 2 O 5  system, dry milled and thermally treated samples under reducing atmosphere exhibit a large paramagnetic component associated to the formation of V 2 O 3  and secondary phases containing V +3  ions; at the same time, an increase of V O  is observed with an abrupt fall of magnetization to  σ ?~?0.7?×?10 −3  emu/gr due to segregation of V oxides and formation of secondary phases. As mechanical milling is an aggressive synthesis method, high disorder is induced at the surface of the ZnO NPs, including V O  and Zn i  depending on the chemical environment. Thermal treatment restores partially structural order at the surface of the NPs, thus reducing the amount of Zn i  at the same time that V 2 O 5  NPs segregate reducing the direct contact with the surface of ZnO NPs. Additional samples were milled for longer time up to 24 h to study the effect of milling on the magnetization; 1-h milled samples have the highest magnetizations. Structural characterization was carried out using X-ray diffraction and transmission electron microscopy. Identification of V O  and Zn i  was carried out with Raman spectra, and energy-dispersive X-ray spectroscopy was used to verify that V did not diffuse into ZnO NPs as well to quantify O/Zn ratios.

Role of vanadium ions, oxygen vacancies, and interstitial zinc in room temperature ferromagnetism on ZnO-V2O5 nanoparticles