Magnetic properties of FeCo-iron oxide core–shell nanoparticles investigated through first order reversal studies

Core–shell magnetic nanoparticles exhibit exchange bias, whereas the magnitude of the exchange bias field is influenced by various factors that are still under investigation. We present a detailed analysis of the magnetic behavior in Fe- and Co-rich FeCo particles with a ferrimagnetic oxide shell. The as-synthesized alloys, with an average particle size above 150 nm, show high saturation magnetization and exhibit multidomain nature. The magnetic behavior has been analyzed through first order reversal studies at room temperature, and low temperature (15 K) for the as-synthesized and size-reduced alloys. The size-reduced alloys exhibit exchange bias that enhances with decreasing average particle size and found to be maximum for the Co-rich FeCo. First order reversal curve (FORC) studies could resolve the reversible, irreversible magnetization components, and magnetostatic interactions. The low-temperature field cooled measurements expose random field bias acting at the interfaces. The studies reveal that FORC could be utilized to obtain information about particle size and its distribution dependent magnetic behavior in core–shell nanostructures.