Evidence by EPR of ferromagnetic phase in Mn-doped ZnO nanoparticles annealed at different temperatures

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• 作者：D. Toloman^a ; A. Mesaros^b ; ^{amalia.mesaros@chem.utcluj.ro} ; A. Popa^a ; O. Raita^a ; T.D. Silipas^a ; B.S. Vasile^c ; O. Pana^a ; L.M. Giurgiu^a
• 关键词：Ferromagnetic phase ; Nanoparticles ; Wet chemical synthesis ; Electron paramagnetic resonance
• 刊名：Journal of Alloys and Compounds
• 出版年：2013
• 出版时间：25 February, 2013
• 年：2013
• 卷：551
• 期：Complete
• 页码：502-507
• 全文大小：865 K

文摘

This paper reports the influence of the temperature annealing (T_a) on the structural, morphological, Raman and EPR characteristics of Mn-doped ZnO nanoparticles. XRD studies reveal a wurzite-type structure, while the formation of ZnMnO₃ secondary phase was evidenced only for the nanoparticles annealed at T_a = 700 ¡ãC. This impurity phase was also identified by Raman scattering in the samples thermally treated at 600 ¡ãC and higher temperatures. TEM investigations reveal that the average particle size of samples starts from 13 nm. With the increase of synthesis temperature, the average particle size reaches a value of 55 nm for 700 ¡ãC. From the XPS spectrum of Mn 2p core-level doublet only the 2+ valence state for manganese ions was evidenced. EPR investigations show that depending on the annealing temperature, Mn ions are incorporated either in the interior of ZnO nanoparticles (T_a = 425 and 500 ¡ãC) or at their surfaces (T_a > 500 ¡ãC). For the sample annealed at T_a = 425 ¡ãC, a new broad resonance line arises, which was attributed to a ferromagnetic phase. We assume that this ferromagnetic phase could be due to the interaction between the Mn²⁺ ions and uncompensated acceptor defects incorporated into the ZnO lattice during the thermal treatment of the samples. Our investigations show that the ferromagnetism in Mn-doped ZnO nanoparticles could appear in the low-temperature annealed samples and disappears in the samples thermally treated at high temperatures.