Observation of room-temperature superparamagnetic behavior of Fe5Si3 nanocrystals synthesized via 50 keV Fe ion implantation in silicon

Nanocrystalline Fe5Si3 structures embedded within the top 50 nm of Si substrate have been synthesized via low-energy (50 keV) Fe- ion implantation and subsequent thermal annealing in vacuum at 500 degrees C for 1 h. Prior to the ion irradiation, the distribution of the implanted ions and sputtering of the implanted and target atoms were modeled using both static and dynamic ion solid interaction simulation codes in order to determine the desired ion implantation experimental parameters. The simulation showed that for a 50 keV Fe ion beam, the concentration of the Fe reaches a saturation value of 48% at a fluence 2 x 10(17) ions/cm(2), while distributed within the top 60 nm from the surface of the Si substrate. Depth profile utilizing X-ray photoelectron spectroscopy spectra along with Ar-ion etching shows the presence of Fe ions buried under the surface of Si. X-ray diffraction pattern confirms the presence of crystalline Fe5Si3 in Si. In the vibrating sample magnetometer analysis, the synthesized Fe5Si3 nanocrystal structures show superparamagnetic behavior with very low magnetization at room temperature.