Effect of Chromium Concentration on the Microstructure and Magnetic Properties of FeCr Nanostructured Powders Prepared by Mechanical Alloying

We have successfully synthesized FeCr nanostructured powders via a high-energy ball milling process. The effect of the chromium (Cr) concentration on the structural, magnetic, and hyperfine properties of Fe100−xCrx (x = 2.5, 7.5, 12.5, 17.5, and 20 at.%) nanostructured powders were investigated. For the low Cr concentrations, the X-ray diffraction results reveal the presence of a single phase which is the centered cubic body (bcc). Beyond 12.5 at.%, the structure shows a mixture of bcc and face-centered cubic (fcc) phases. The value of the lattice parameter of the bcc-FeCr phase gradually increases as the Cr concentration increases, reaching a maximum of 2.8776 Å. With the exception of the lowest Cr concentration (2.5 at.%), we note that the mean grain size, < D(nm) > , linearly decreases down to around 57 nm when the Cr concentration is increased; the same behavior was observed for the mechanically induced microstrain, ε (%). The addition of Cr strongly affects the value of the saturation magnetization (MS), i.e., the saturation magnetization monotonously decreases with increasing Cr concentration. However, the coercive field (HC) increases up to 54 Oe as the Cr concentration is increased. The Mössbauer results confirm those obtained by XRD analysis and show a clear influence of Cr concentration on the hyperfine magnetic field < Bhf > and consequently on the local environment of iron atoms.