Microemulsion Synthesis of Nd 0.5 Ca 0.5 MnO 3 and Nd 0.5 Sr 0.5 MnO 3 Nanoparticles
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Microemulsion Synthesis of Nd0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3 Nanoparticles Z. Q. Wang1, K. B. Yin1, F. Gao1, K. F. Wang1, Z. F. Ren2, and J. -M. Liu1,3 1 Department of Physics, Nanjing University, Nanjing, 210093, China, People's Republic of 2 Department of Physics, Boston College, Boston, MA, 02467 3 International Center for Materials Physics, Chinese Academy of Sciences, Shenyang, 110016, China, People's Republic of
ABSTRACT Nd0.5Ca0.5MnO3 (NCMO) and Nd0.5Sr0.5MnO3 (NSMO) nanoparticles have been synthesized using microemulsion synthesis method, with hexamethylene alkyl, a mixture of OP and 1hexanol, NaOH as oil phase, surfactant, and precipitating agent, respectively. The phase formation of NCMO and NSMO nanoparticles was examined. The final NCMO and NSMO nanoparticles have average particle size of 24 and 50 nm, respectively, and present high-quality crystallinity. Measurements of the magnetic properties suggest that the charge-order state favored for bulk NCMO phase collapses in NCMO nanoparticles. The spin freezing behavior for both NCMO and NSMO nanoparticles was identified. INTRODUCTION Hole doped perovskite manganites with general formula R1-xAxMnO3 (R=Rare earth ion, A=Alkali earth ion) have attracted considerable attention because of their unusual magnetic and electronic properties (e.g. colossal magnetoresistance and charge ordering) and potential technological applications (e.g. high density magnetic storage and field sensors) [1-5]. Several techniques for the preparation of these manganites, including conventional solid-state sintering [3,5], sol-gel [6,7], and hydrothermal reaction [8-10], have been examined. The conventional solid-state sintering needs high reaction temperature (usually as high as 1400oC), complex operating procedures. Furthermore, the products obtained have large particle size of several micrometers. In comparison with solid-state sintering, sol-gel and hydrothermal methods possess advantages such as low reaction temperature, simple operating procedures etc. In addition, nanostructured manganites can be produced using these two methods. However, the sol-gel method has low yield of products because of the need of template providing nanochannels for the growth of manganites. Though hydrothermal synthesis is performed under a temperature below 240oC and have been successfully applied to the preparation of many ternary or binary oxides, only a very limited number of doped manganites can be synthesized by this method and most of the products have particle sizes as large as several micrometers [9,10]. Microemulsion synthesis has been used to prepare nanosized binary and ternary oxides such as TiO2, LaMnO3, ZnAl2O4, PbZrO3 [11-13]. In a typical microemulsion synthesis, an oil phase, a surfactant phase and an aqueous phase are mixed, resulting in a microemulsion system consisting of numerous nanosized aqueous droplets due to the uniform dispersion of the aqueous phase in the continuous oil phase. Precipitating reactions occur when the aqueous droplets containing desirable reacta
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