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 Fe_100−xCr_x (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 (M_S), i.e., the saturation magnetization monotonously decreases with increasing Cr concentration. However, the coercive field (H_C) 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 < B_hf > and consequently on the local environment of iron atoms.