Tuning Exchange Bias in\nCore/Shell FeO/Fe₃O₄ Nanoparticles

Abstract

Monodisperse 35 nm FeO nanoparticles (NPs) were synthesized\nand\noxidized in a dry air atmosphere into core/shell FeO/Fe₃O₄ NPs with both FeO core and Fe₃O₄ shell dimensions controlled by reaction temperature and time. Temperature-dependent\nmagnetic properties were studied on FeO/Fe₃O₄ NPs obtained from the FeO NPs oxidized at 60 and 100 °C for\n30 min. A large exchange bias (shift in the hysteresis loop) was observed\nin these core/shell NPs. The relative dimensions of the core and shell\ndetermine not only the coercivity and exchange field but also the\ndominant reversal mechanism of the ferrimagnetic Fe₃O₄ component. This is the first time demonstration of tuning\nexchange bias and of controlling asymmetric magnetization reversal\nin FeO/Fe₃O₄ NPs with antiferromagnetic core\nand ferrimagnetic shell.