Synthesis of controlled-chemistry ultrafine FexNi1−x ferromagnetic powders

We show that the synthesis of ultrafine FeNi particles can be achieved by an evaporation and cryo-condensation process. Particular attention is paid to the deviation in composition of the as-formed nanocrystalline powders with respect to their master alloys. The trend is that powders are enriched in Ni when composition of the master alloys is FexNi1−x with x < 0.295, and enriched in Fe with x > 0.295. The composition x = 0.295 is of particular interest since it can be produced in large amounts with no deviation in composition. Characterization techniques show that powders are formed of spherical particles with an average grain size of about 55 nm. Specifically, electron energy loss spectroscopy (EELS) was used to confirm the chemical homogeneity inside the particles. Such small particles are pyrophoric in air and we have successfully stabilized the powders by soft oxidation. EELS was also used to examine the nature of the layer oxide with respect to the particle composition. The synthesis technique and knowledge about structure and chemical composition of these FeNi nanoparticles is of particular importance for the design of miniaturized data recording and data probe devices.