Exchange Bias in Chemically Reduced FeCo Alloy Nanostructures
Résumé
The equiatomic FeCo alloy with average particle sizes of 140 and 30 nm is obtained using an instant chemical reduction process. The mean hyperfine field of 36.0(5) T estimated from 300 K 57Fe Mössbauer spectra is consistent with a disordered FeCo phase with a relative fraction of 90(2)% for both the samples, along with γ-Fe2O3. A CoO shell with an average thickness of 2.7 nm is inferred from transmission electron microscopy in the size-reduced FeCo. The room temperature coercivity of the size-reduced FeCo is higher than the expected theoretical values. An exchange bias field (HE of 296 Oe), vertical remanence shift at 15 K, and an exchange bias blocking temperature of 150 K are exhibited by the 30 nm FeCo particles. The observed HE and its temperature dependence are fairly explained based on a random field model.