Sol-Gel Magnetic Materials

Lucia Gutierrez, Sabino Veintemillas-Verdaguer, Carlos J. Serna, and Maria del Puerto Morales 

The existence of a number of metal alkoxides suitable as sol-gel precursors for many oxide powders, such as silica or titanium oxide, and the compositional variability available are the main advantages of sol-gel procedures. However, for metal alkoxides with low valence, such as Fe, the hydrolysis and condensation are too rapid to control particle size and shape. Usually, magnetite and ferrites are preferably obtained by hydrolysis of metal salts such as acetates or citrates in water, ethanol, or glycol. The counterions work as a pH buffer and as a component of the precursor complexes. The conditions need to be chosen carefully to yield a material with appropriate properties for each specific application. Disadvantages of the sol-gel methods include contamination from reaction by-products, as well as the need for posttreatment of the products. 

Conventional synthesis of magnetic nanoparticles, well described in the scientific literature, includes a variety of thermal decomposition and solvothermal methods and a number of coprecipitation reactions [3-5]. Although these methods yield high-quality magnetic materials, many exhibit drawbacks associated with extreme reaction conditions. The controlled low-temperature 

The Sol-Gel Handbook Synthesis, Characterization, and Applications, First Edition. 

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This chapter is intended to cover major aspects of the deposition of metals and metal oxides and the growth of nanosized materials from metal enolate precursors. Included are most types of materials which have been deposited by gas-phase processes, such as chemical vapor deposition (CVD) and atomic layer deposition(ALD), or liquid-phase processes, such as spin-coating, electrochemical deposition and sol-gel techniques. Mononuclear main group, transition metal and rare earth metal complexes with diverse /3-diketonate or /3-ketoiminate ligands were used mainly as metal enolate precursors. The controlled decomposition of these compounds lead to a high variety of metal and metal oxide materials such as dense or porous thin films and nanoparticles. Based on special properties (reactivity, transparency, conductivity, magnetism etc.) a large number of applications are mentioned and discussed. Where appropriate, similarities and difference in file decomposition mechanism that are common for certain precursors will be pointed out. 

Colomban, R, and Vendange, V., Sol-gel routes towards magnetic nanocomposites with tailored microwave absorption, in Nanophase and Nanocomposite Materials II, S. Komameni, J.C. Rarker, and H.J. Wollenberger, eds.. Mater Res. Soc. Symp. Proc., 457, 451, 1997. 

In the fifteen years since publication of the first edition of Comprehensive Coordination Chemistry (CCC, 1987), group 5 chemistry has been part of the intensive development of ceramic, optical, and magnetic materials based upon metal borides, nitrides, phosphides, oxides, and sulfides. A major impetus came from the discovery of the high-temperature superconducting oxides. In addition, the search for new routes to these materials via sol-gel or chemical vapor deposition techniques has spurred growth in metal amido, oxo, alkoxo, thio, and carboxylato chemistry. 

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