Facile synthesis of superparamagnetic Ni-Fe ultrafine nanoalloy nanoparticles with equilibrium ordered phase structure via a sol-gel process.

Ni-Fe nanoalloy nanoparticles with an average grain size of 4 nm in diameter have been prepared by a sol-gel method under a hydrogen atmosphere where ethanol and oleic acid have been used as solvent and surfactant, respectively. X-ray diffraction (XRD) and selected area electron diffraction (SAED) examinations of the nanoparticles show the occurrence of (111), (200), (220) and (311) diffraction peaks and rings, meaning that the nanoparticles have a face-centered-cubic phase structure. Moreover, a superlattice diffraction peak and a diffraction ring/spot can also be observed in XRD and SAED results, indicating the formation of an equilibrium ordered L1(2) phase structure. The as-prepared Ni-Fe nanoalloy particles show typical superparamagnetic behavior at room temperature and the blocking temperature of the nanoparticles is determined to be about 50 K.