Magnetic enhancement of carbon-encapsulated magnetite nanoparticles

In this paper, we report the effect of carbon encapsulation on the magnetic behavior of magnetite (Fe3O4) nanoparticles obtained through chemical coprecipitation. Using starch, Fe3O4/carbon core–shell nanoparticles were produced through a hydrothermal method. Magnetic studies revealed that both the Fe3O4 and Fe3O4/carbon core–shell nanoparticles were nearly superparamagnetic at room temperature; more importantly, carbon encapsulation significantly enhanced the room-temperature ferrimagnetism. Transmitting optical magnetic circular dichroism analysis indicated the existence of interfacial charge transfer in the Fe3O4/carbon heterosystem. The ferrimagnetic enhancement was attributed to the charge transfer to polarized states of the A-site in Fe3O4, which is equivalent to chemical reduction of the A-site irons of Fe3O4. We concluded that Fe3O4/carbon core–shell nanoparticles formed a heterosystem so that the amorphous carbon passivated the magnetic semiconducting Fe3O4 nanoparticles, to which the sp2 electron was transferred. •Room-temperature ferrimagnetic enhancement was observed for carbon-encapsulated magnetite NPs.•Process temperature and the amount of starch precursor used in coprecipitation process was found to be crucial.•VSM and OMCD measurement have revealed interfacial charger transfer engendered the magnetic enhancement.•Chemical reduction of the A-site irons of Fe3O4 caused by carbon-encapsulation was attributed to the observed magnetic enhancement.