Superparamagnetic Reduced Graphene Oxide

Superparamagnetic Reduced Graphene Oxide

Author: Jonathan Faiz

The synthesis of graphene-based systems that show large magnetoresistive effects at ambient temperatures remains a challenge. Changzeng Wu and a team from the Chinese Academy of Sciences and the University of Science & Technology of China have developed a strategy for the fabrication of a superparamagnetic reduced graphene oxide with a large, low-field negative magnetoresistance at room temperature.

Reduced graphene oxide (rGO) possesses nontrivial sp-electron magnetism. Introduction of functional groups covalently bound to the carbon framework can result in ferromagnetism. Wu´s team modified rGo with thiol groups by reaction with H2S gas. This rGO with a high sulfur concentration is ferromagnetic. Mild oxidation with oxygen gas resulted in partial removal of the thiol groups, and led to a rGO with low sulfur concentration (LS-rGO) that is superparamagnetic. The magnetic behavior changes as the number of unpaired spins decreases and the magnetic domains reach a critical size as the number of thiol groups is reduced and thus interact less.

Further studies showed that LS-rGO has a large low-field negative magnetoresistive effect at room temperature (–8.6 %; 500 Oe; 300 K). This phenomenon occurs as the independent ferromagnetic domains align in the presence of an external magnetic field, and this results in an increased electron-tunneling probability.


 

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