Abstract

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 Fe-57 Mossbauer spectra is consistent with a disordered FeCo phase with a relative fraction of 90(2)% for both the samples, along with gamma-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 (H-E 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 H-E and its temperature dependence are fairly explained based on a random field model.