Fabrication and Characterization of Fe100-xNix Nanoparticles in the Invar Region

In this work, Fe100-xNix nanoparticle systems in the invar region (x = 29, 32, and 37) were prepared by the method of chemical co-precipitation. X-Ray Diffraction (XRD) patterns confirmed the coexistence of both bcc and fcc phases for x = 29 and 32. However, only fcc phase was observed for x = 37. Scanning Electron Microscope (SEM) images indicated that the particle size is ~ 120-500 nm, and is almost independent of x. M\"ossbauer spectroscopy (MS) on the prepared nanoparticles indicated the development of a paramagnetic phase characteristic of the low-spin (antitaenite) fcc phase, in addition to the magnetic components characteristic of the bcc phase and the high-spin fcc phases. Since it is not possible to resolve the low- spin fcc phase from the high-spin fcc phase in XRD patterns, MS proves to be an effective tool for studying the prepared nanoparticle systems.