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    Defect-mediated ferromagnetism in ZnO:Mn nanorods
    (Springer, 2014) Yilmaz, S.; McGlynn, E.; Bacaksiz, E.; Bogan, J.
    In this work, the structural, chemical and magnetic properties of ZnO:Mn nanorods were investigated. Firstly, well-aligned ZnO nanorods with their long axis parallel to the crystalline c-axis were successfully grown by the vapor phase transport technique on Si substrates coated with a ZnO buffer layer. Mn metal was then diffused into these nanorods at different temperatures in vacuum. From SEM results, ZnO:Mn nanorods were observed to have diameters of similar to 100 nm and lengths of 4 mu m. XPS analysis showed that the Mn dopant substituted into the ZnO matrix with a valence state of +2. Magnetic measurements performed at room temperature revealed that undoped ZnO nanorods exhibit ferromagnetic behavior which may be related to oxygen vacancy defect-mediated d (0) ferromagnetism. ZnO:Mn samples were seen to show an excess room temperature ferromagnetism that is attributed to the presence of oxygen vacancy defects forming bound magnetic polarons involving Mn.
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    Synthesis and characterization of Mn-doped ZnO nanorods grown in an ordered periodic honeycomb pattern using nanosphere lithography
    (Elsevier Sci Ltd, 2014) Yilmaz, S.; Garry, S.; McGlynn, E.; Bacaksiz, E.
    We report a study of the structural, optical and magnetic properties of undoped and Mn-doped ZnO nanorods grown by chemical bath deposition in a periodic honeycomb lattice formation. Mn-doping is accomplished by a diffusion process at a constant time of 8 h for different temperatures of 500 degrees C, 600 degrees C and 700 degrees C. Undoped and Mn-doped ZnO nanorods had a hexagonal wurtzite structure with a (0 0 2) preferred orientation. From SEM results, it was seen that Mn-doped ZnO nanorods grew vertically in the honeycomb lattice with lengths of 0.8 mu m. XPS results showed that Mn3+ ions was successfully incorporated in the ZnO matrix by substituting for Zn2+ ions and that Mn-doping increased the number of oxygen vacancies in ZnO compared to undoped ZnO. This result was also supported by photoluminescence data at 10 K. Magnetic data showed that all the samples exhibited ferromagnetic character. Although the origin of undoped ZnO is related to oxygen vacancy-induced d(0) ferromagnetism, bound magnetic polarons are responsible from the ferromagnetism of Mn-doped ZnO samples which have T-c values above the room temperature. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.