Magnetic nanocrystals

The morphologies of magnetic multicomponent nanocrystals can be subdivided into several groups, namely core hdl nanoparticles, dumbbell nanopartkles, and the more recently discovered hollow nanostructures. The general approach towards the 

---

This review has covered many of the essential features of the physical chemistry of nanocrystals. Rather than provide a detailed description of the latest and most detailed results concerning this broad class of materials, we have instead outlined the fundamental concepts which serve as departure points for the most recent research. This necessarily limited us to a discussion of topics that have a long history in the community, leaving out some of the new and emerging areas, most notably nonlinear optical studies [152] and magnetic nanocrystals [227]. Also, the... 

Majetich and coworkers have studied magnetic properties of carbon-coated Co[32], Gd2C3, and FIo2C3 nanocrystals[33] formed in the chamber soot. A brief account on the coated Co nanocrystals is given here. They extracted magnetic nanocrystals from the crude soot with a magnetic gradient field technique. 

Redl, F. X., Cho, K. S., Murray, C. B. O Brien, S. Three-dimensional binary superlattices of magnetic nanocrystals and semiconductor quantum dots. Nature (London) 423, 968—971 (2003). 

Closely spaced magnetic nanocrystals that are found in nature are often more perfect in their sizes, shapes and arrangements than their synthetic counterparts. As a result, they can be chosen as model systems to study the effect of particle size, morphology, crystallography and spacing on magnetic microstructure. 

In this paper, we present AFM investigation of the above mentioned processes. An application of PAA for fabrication of magnetic nanocrystals and carbon nanotubes is demonstrated. A possibility of terabit memory production with PAA templates and nanomasks is analyzed. 

Song HT, Choi JS, Huh YM, Kim SJ, Jun YW, Suh JS, Cheon JW (2005) Surface modulation of magnetic nanocrystals in the development of highly efficient magnetic resonance probes for intracellular labeling. J Am Chem Soc 127 9992-9994... 

Figure 3.114 Schematic representation of the hot injection technique usually employed in the organometallic synthesis of magnetic nanocrystals. A thermocouple (TC) controls the...

As shown above, the optimized combination of precursors (C0Q2, Co(CH3COO)2 or Co2(CO)8) and reducing agents (superhydride or polyalcohol) allows the selective preparation of monodisperse cobalt nanoparticles with a desired crystalline phase. Such behavior shows that the solution-phase chemical synthesis of magnetic nanocrystals is not thermodynamically controlled, and thus can allow the preparation of crystal phases that are metastable, such as the e-Co structure [9]. The control of size and the crystalline phase of nanoparticles is important, as these parameters greatly affect the magnetic properties (see Section 3.3.2.5). 

Hollow Magnetic Nanocrystals Hollow nanoscale stmctures were first obtained by Y. Yin during the sulfurization of cobalt nanocrystals at elevated temperatures [145]. This process was found to lead to the formation of hollow cobalt sulfide nanocrystals such that, depending on the size of the cobalt nanocrystals and the cobalt sulfur molar ratio, different stoichiometries of hollow cobalt sulfide could be obtained. Hollow nanostmctures are usually formed through the nanoscale Kirkendall effect, which is based on the difference in diffusion rates of two species, and results in an accumulation and condensation of vacancies [146]. This phenomenon was first observed by Kirkendall at the interface of copper and zinc in brass in 1947 [147]. As a typical example of the nano-Kirkendall effect, the controllable oxidation of iron nanoparticles by air can lead to the formation of hollow iron oxide nanostructures, as shown in Figure 3.137. During the course of metal nanoparticle oxidation, the outward diffusion of metal occurs much faster in... 

Thermal decomposition In order to control shape and size more precisely, the method of thermal decomposition is developed. This is a method similar to the synthesis of semiconductors with high-quality nanocrystals. The smaller magnetic nanocrystals can be formed from organometallic compounds in organic solvents. By adding precursor in zerovalent, thermal decomposition will have metal formed in the end. When the decomposition happens, cationic metal will lead the electrons to the oxides and the reaction solution will have metal acid salts in nonaqueous solution. With the metal fatty acid compound in the solution, the metal will reach saturation and the metal magnetic... 

---