Exchange Bias in Chemically Reduced FeCo Alloy Nanostructures

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 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.

Comprehensive Law‐of‐Approach‐to‐Saturation for the Determination of Magnetic Anisotropy in Soft Magnetic Materials

“…The presence of γ-Fe 2 O 3 is in concordance with the results of Mössbauer spectrometry analysis of the particles prepared under similar synthesis conditions. [58] The difference between the binding energy of 2p 3/2 state and that of its satellite peak in case of γ-Fe 2 O 3 is around 8 eV, which is in line with the values obtained for the 110 and 20 nm sample. [64] The XPS spectra of the particles obtained through terminal polyol are devoid of the satellite peak and Fe 0 indicating Fe 3 O 4 as the major fraction.…”

“…A thin layer of iron oxide is inevitable in case of Fe even with particles greater than 100 nm, which is not reflected in XRD due to their lower fraction or poor crystallinity. [58,59] However, particles synthesized using terminal polyols such as t-PG and t-BG showed Fe 3 O 4 /γ-Fe 2 O 3 peaks with a minor Fe peak (Figure S1f and g, Supporting Information). Fe 3 O 4 and γ-Fe 2 O 3 has similar spinel structure and hence it is difficult to distinguish the phase through XRD.…”