Large exchange bias in Cr substituted Fe₃O₄ nanoparticles with FeO subdomains

Tuning the anisotropy through exchange bias in bimagnetic nanoparticles is an active research strategy for enhancing and tailoring the magnetic properties for a wide range of applications. Here we present a structural and magnetic characterization of unique FeCr-oxide nanoparticles generated from seed material with a Fe : Cr ratio of 4.71 : 1 using a physical aerosol method based on spark ablation. The nanoparticles have a novel bimagnetic structure composed of a 40 nm ferrimagnetic Cr-substituted Fe₃O₄ structure with 4 nm antiferromagnetic FeO subdomains. Cooling in an applied magnetic field across the Néel temperature of the FeO subdomains results in a significant shift in the hysteresis, demonstrating the presence of a large exchange bias. The observed shift of μ₀H_E = 460 mT is among the largest values reported for FeO-Fe₃O₄-based nanoparticles and is attributed to the large antiferromagnetic-ferrimagnetic interface area provided by the subdomains.