The shell thickness dependence of the exchange bias of Fe/Fe3O4 core-shell nanoparticles

Exchange bias (EB) effect has been intensively studied for more than half century due to its applications in spintronics devices, such as giant magneto resistance (GMR) read heads and magnetic random access memory (MRAM).[1] Except for conventional ferromagnetic (FM)-antiferromag-netic (AFM) system, EB has also been reported in other magnetic systems, such as ferromagnetic (FM)-ferromagnetic (FIM) system, spin glasses (SG) and nanoparticles with surface spin disorder. The most studied FM-FIM system is the Fe/Fe₃O₄ core shell structure. It is believed that the inter-facial SG state plays a major role in the EB of this system.[2,3] However, all the studies have aimed to the stably oxidized Fe nanoparticles. The effect of the FIM thickness on the EB in this system has been neglected. In this study, a controlled oxidizing procedure was adopted to obtain Fe/Fe₃O₄ nanoparticles with different Fe₃O₄ thickness. The Fe₃O₄ thickness dependence of the EB was studied.