Zhengzhou University researchers have synthesized a new material that combines graphene's remarkable properties with a strong response to magnetic fields.
Graphene has a long spin lifetime and hyperfine interactions, making it potentially favorable for spintronics applications. Despite the recent discoveries of spin-containing graphene materials, graphene-based materials with room-temperature macroscopic ferromagnetism are extremely rare. In their recent study, room-temperature ferromagnetic amorphous graphene oxide (GO) was synthesized by introducing abundant oxygen-containing functional groups and C defects into single-layered graphene, followed by a self-assembly process under supercritical CO2 (SC CO2).
Such amorphous GO exhibits the highest saturation magnetization (1.71 emu g−1) and remanent magnetization (0.251 emu g−1) compared to the rest of metal-free graphene-based materials at room temperature. Experimental and theoretical investigations attribute such strong ferromagnetism to the bridging of the adjacent graphene layers though the out-of-plane oxygen-containing groups, which leads to asymmetric lattices with large net magnetic moments.
To address graphene’s lack of ferromagnetism, the scientists synthesized a new hybrid material, incorporating multiple layers of carbon atoms along with hydrogen and oxygen atoms. They achieved this by subjecting graphene to carbon dioxide under pressures more than a hundred times higher than atmosphere, which not only forced it to bond with the graphene layers but also infused oxygen atoms into the crystalline structure. Hydrogen atoms came from hydrogen peroxide present as a byproduct during this process.
The magnetic properties of electrons depend greatly on how they interact with their atoms. By deforming the material’s crystal lattice or adding additional atoms its properties can be manipulated, and this is exactly what the authors achieved. Their modification of graphene’s structure led to the necessary changes in the properties of electrons, making them more susceptible to an applied magnetic field.
“We have synthesized amorphous graphene oxide with room-temperature ferromagnetism by introducing abundant oxygen-containing groups and defects into monolayer graphene, which are further self-assembled with the assistance of supercritical carbon dioxide,” said Qun Xu, a professor at Zhengzhou University in China and lead author of the study.
An essential component of this study, in contrast to conventional approaches, is the fact that the team did not have to rely on metals to induce magnetism in graphene, as their scarcity and environmental impact pose challenges to sustainability.
The team believes that the material they have obtained will find its way into electronics in the near future, accepting that there are also difficulties along the way that will need to be overcome.
“We’re doing our best to put it into practice, maybe in the next 3–5 years,” said Xu. “Large scale production is the remaining hurdle.”
Beyond its technological implications, the study holds significance in the realm of carbon capture as it uses and traps carbon dioxide — a potent greenhouse gas. By repurposing CO2 in processes like this, researchers could potentially positively contribute to net zero targets.
“In the future, besides the fascinating room-temperature graphene oxide, we hope to use CO2 to obtain more interesting materials,” concluded Xu.