Interfacial Anisotropy‐Induced Enhanced Exchange Bias in FeCo Alloy Nanoparticles

The mechanism of exchange bias in Fe‐based nanoparticles is obscure as the role of the interface is unclear. This study explores the exchange bias characteristics in FeCo alloy nanoparticles of various compositions and an average particle size of 10 nm embedded in an oxide layer. The presence of CoO and γ‐Fe 2 O 3 in all the FeCo compositions is confirmed from the phase analysis. The ferromagnetic resonance analysis reveals substantial effective magnetic anisotropy values in all the samples attributed to the surface and interfacial anisotropies. Significant enhancements in the ferromagnetic resonance linewidth and magnetic anisotropy are observed for the Fe 40 Co 60 and Fe 60 Co 40 nanoparticles, respectively. The Fe 60 Co 40 nanoparticles exhibit a high exchange bias field ( H E ) of 1.2 kOe at 15 K, attributed to the antiferromagnetic interfaces. The ferromagnetic resonance studies, field‐cooled hysteresis loops, and the random field model suggest a comprehensive explanation for the observed increase in H E .