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| STRUCTURE AND MAGNETIC BEHAVIOR OF Zn1−xCoxO CRYSTAL POWDERS PREPARED BY SOL–GEL TECHNIQUE |
| GAO Qian, SUN Benzhe, QI Yang, QI Lianzhong |
| College of Sciences, Northeastern University, Shenyang 110819 |
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Cite this article:
GAO Qian SUN Benzhe QI Yang QI Lianzhong. STRUCTURE AND MAGNETIC BEHAVIOR OF Zn1−xCoxO CRYSTAL POWDERS PREPARED BY SOL–GEL TECHNIQUE. Acta Metall Sin, 2011, 47(3): 337-343.
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Abstract ZnO–based diluted magnetic semiconductors (DMSs) have been considered as one of the promising candidates for fabricating DMSs due to their initial prediction in theory of having the Curie temperature greater than room temperature, its high solubility for transition metals, and its superior semiconductor properties. Recently, Co substituted ZnO DMSs were reported frequently to show ferromagnetic properties at room temperature. However, various subsequent studies do not seem to converge on the origin of room–temperature ferromagnetism. Among the controversy, Co–cluster, Co–oxides and substitutions of Co for Zn are typical viewpoints. Meanwhile, it is not completely understood how the fabricating process influence the magnetic properties of Co–doped ZnO DMS. For this purpose, relationships among Co–doping concentration, sintered temperature, microstructure and magnetic properties of ZnO need to be invesigated particularly. In this paper, Zn1−xCoxO (x=0.01,0.02, 0.03, 0.04 and 0.05, atomic fraction) nanocrystal powders were prepared by sol–gel technique. The crystal structure, lattice parameters, orphology and composition were characterized and analyzed by XRD, TEM, SEM and EDS, respectively. The magnetic properties were examined at room temperature sing a vibrating sample magnetometer (VSM). It can be found that all the samples are composed of the particles with hexagonal wurtzite structure and the sizes of the particles are about 100 nm. For all synthesized Zn1−xCoxO samples, the lattice constants are smaller than those of un–doping ZnO crystals under the condition of the same sintered temperature. It indicates Co2+ ions have substituted Zn2+ sites. All the samples exhibit room–temperature ferromagnetic characteristics, and the ferromagnetism is their intrinsic attribute, in which the Zn0.98Co0.02O sample sintered at 500 and 700 ℃ has the highest coercivity (Hc) of 334.02 Gs and the highest remanent magnetization ratio (Mr/Ms) of 0.1813, respectively, and the Zn0.96Co0.04O sample sintered at 950 ℃ has the maximum magnetic energy product (BH) of 1.764×10−4 J/kg ad saturation magnetization (Ms) of 0.5583 Am2/kg. he magnetic behaviors of tese samples vary not only with the cocetration of Co, but also with the size of crystal grains and te concentration of oxygen vacacies. It can be found that the moderate Co content and the lager size of crystal grains are in favour of increasing room–temperature ferromagnetic characteristics. Meawhile, as far as the same concentration of Co is concened, the smaller volume of the cecontributes to increase room–temperature ferromagnetism.
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Received: 12 October 2010
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| Fund: Supported by Science Research Program of Liaoning Province (No.200822208) and Shenyang Municipal Science Research Program (No.1091139–9–00) |
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