Alloys superparamagnetism

Iron-platinum alloy nanoparticles are very promising candidates for future data storage systems. They become available by simultaneous reduction of platinum acetylacetonate and the decomposition of Fe(CO)5 in oleic acid and oleyl amine.The composition of FexPti x can be varied between X = 0.48 and x = 0.7. The particles exhibit disordered fee structure. They are superparamagnetic at room temperature. Aimealing at 550-600 °C transforms the fee structure into a face-centered tetragonal (fet) one. These have been shown to be suited for storage devices owing to their room temperature coercivity. The exact transition temperature depends on the stoichiometry. 

Xu J, Hickey BJ, Howson MA, Greig D, Cochrane R, Mahon S, Achilleos C, Wiser N (1997) Giant magnetoresistance in AuFe alloys Evidence for the progressive unblocking of superparamagnetic particles. Phys Rev B 56 14602-14606... 

Kok] Kokorin, V.V., Perekos, A.E., Chmstov, K.V., Early Stages of Decomposition and Superparamagnetism of Copper-Nickel-Iron Alloy (in Russian), Metallofizika, 67, 35—41 (1977) (Experimental, Magn. Prop., Kinetics, 11)... 

The pyrolysis of polyferrocenylsUanes within the channels of the mesoporous silica MCM-41 and the creation of nanostructured magnetic ceramic nanocomposite materials has also been achieved [127]. In addition, the use of sacrificial porous alumina templates yields organometallic and magnetic ceramic nanofibers [128]. Hyperbranched polyferrocenylsUanes have also been synthesized, and pyrolysis of these interesting materials has been found to lead to superparamagnetic ceramics [129]. Furthermore, pyrolysis of polyferrocenylsUanes with pendant Co clusters yields ceramics containing hybrid Fe/Co alloy nanopartides [130]. 

Fe and 86% Cu atoms, i.e. less Fe atoms than added in the starting compositions. A Fe Mossbauer spectroscopic study also indicated the formation of a Fe-Cu alloy with less Fe than expected (as above). Incomplete reduction of iron was apparent from these results. The product exhibited superparamagnetism. 

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