Magnetic Properties of Co Nanoparticles in an AlMCM41 Mesoporous Host
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Magnetic Properties of Co Nanoparticles in an AlMCM41 Mesoporous Host Jin-Seung Jung1,5 , Jun-Yong Kim1, Weon-Sik Chae2, Yong-Rok Kim2, Jong-Ho Jun3, Leszek Malkinski4, Weilie Zhou5, Amar Kumbhar5, Marilena L.Viciu5, John B. Wiley5, Charles J. O’Connor5 1 Department of Chemistry, Kangnung National University, Kangnung 210-702, South Korea 2 Department of Chemistry, Yonsei University, Seoul 120-749, South Korea 3 Department of Applied Chemistry, Konkuk University, Chungju 380-701, South Korea 4 Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa, Poland 5 Advanced Material Research Institute/ Department of Chemistry, University of New Orleans, LA 70148, USA ABSTRACT Ultrafine cobalt particles in AlMCM41 silica tubes have been synthesized by ion exchange and the reduction with sodium borohydride. The role of this stable host matrix of AlMCM41 silica is to prevent agglomeration of the magnetic particles attached to the walls of AlMCM41 silica pores. The size of the host pores naturally limits the particle dimensions and thus improves their size distribution. Both magnetic susceptibility measurements and transmission electron microscopy (TEM) show a narrow distribution size of the nanoparticles. Well controlled insertion of the magnetic material to the host channel excludes formation of bulk particles outside the host material grains, which was confirmed by the TEM studies. X-ray diffraction data did not show peaks corresponding to a crystalline cobalt, but this maybe due to small size of particles and their relatively small volume fraction. The content of Co in the AlMCM41 host was measured using both magnetic measurements and elemental analysis. INTRODUCTION The search for new magnetic materials with unusual chemical and physical properties pushes the need for nanoparticles. A wide variety of chemical methods have been used to synthesize ultrafine particles such as precipitation[1], reduction[2], hydrothermal reaction[3], pyrolysis[4], and core-shell[5]. Among these, the use of porous materials as host for limiting the growth of clusters inside their pores is a relatively promising scheme. The MCM41 material is a nanosized porous silica tubes with a hexagonal honeycomb structure[6]. This ordered channel structure has the advantage of preventing particle agglomeration and allowing control over the particle size. We have synthesized Co nanoparticles using the ion exchange and reduction method in AlMCM41 silica tubes, with aluminum incorporated into the framework of MCM41 because purely siliceous MCM41 did not show the ion exchange capacity[7]. In our recent report we have described the insertion reaction of Ni nanoparticles in AlMCM41 host[8]. As part of our continuing effort to understand the structure and magnetism of ultrafine magnetic materials, we have synthesized cobalt nanoparticles in AlMCM41 host material. Experimental results show that the cobalt particles were confined in the channels of the AlMCM41 host. EXPERIMENTAL SECTION Materials All chemicals were purchased and used without further purifi
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