Fe-Pt alloy nanocrystals

The tendency of monodisperse nanocrystals to arrange into ordered three-dimensional arrays extending to a few microns has been noticed [117]. Careful tuning of crystallization conditions have yielded crystallites of micrometer dimensions consisting of AU55 nanocrystals and Fe-Pt alloy nanocrystals (4.5 nm) [118, 119]. However, it was observed that the nanocrystal arrangement in all the above crystallites was polymorphous. It is believed that such crystallites, consisting of ordered nanocrystals, could prove to be the best candidates to study the collective properties of an ensemble of nanocrystals. 

Colloids of alloys have been made by the chemical reduction of the appropriate salt mixture in the solution phase. Thus, Ag-Pd and Cu-Pd colloids of varying composition have been prepared by alcohol reduction of mixtures of silver nitrate or copper oxide with palladium oxide (Vasan and Rao 1995). Fe-Pt alloy nanocrystals have been made by thermal decomposition of the Fe and Pt acetylac-etonates in high-boiling organic solvents (Sun et al. 2000). Au-Ag alloy nanocrystals have been made by co-reduction of silver nitrate and chloroauric acid with sodium borohydride (Sandhyarani et al. 2000 He et al. 2002). 

The ability to synthesize lattices of nanociystals have led to explorations of their collective physical properties. Thus, it is observed in the case, of Co nanociystals (5.8 nm) that, accompanying lattice formation, the blocking temperature increases. 421 FePt alloy nanocrystals yield ferromagnetic assemblies for which the coerrivity is tunable by controlling the parameters such as Fe Pt ratio and the particle size.1431 The evolution of collective electronic states in CdSe nanocrystals have been followed by optical spectroscopic methods. Compared with isolated nanocrystals, those in the lattice exhibited... 

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