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Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, has seen significant applications in spintronics. Graphene exhibits a long spin lifetime, which refers to how long an electron retains its spin state, and high electron mobility, which allows electronics to move quickly. These factors are essential for spintronics, a field that explores using electron spin for information processing.
However, raw graphene, lacking a local magnetic moment, is diamagnetic. The local magnetic moment, a crucial aspect in spintronics, refers to the magnetic strength and orientation of an atom or ion. Its absence in graphene significantly hinders its application in spintronics.
There are several reasons why it is challenging to achieve ferromagnetism in graphene, including its unique electronic structure of graphene, which makes it difficult to manipulate its magnetic properties. The electrons in graphene are highly localized, which means that they can move freely throughout the material. Unlike transition metal atoms or ions, graphene has no inherent magnetic moment.
Graphene is non-magnetic, so specific modifications are required, including ferromagnetism. Some approaches involve the introduction of chemical doping of nitrogen atoms through N-doping to enhance the magnetization of graphene oxide (GO). However, some advancements still need to achieve room-temperature ferromagnetism in graphene-based materials.
In this article, we will delve into the research paper “Room-Temperature Macroscopic Ferromagnetism in Multilayered Graphene Oxide,” which explains how out-of-plan oxygen groups and sublattice imbalance structures contribute to graphene’s magnetism.
Approach to making graphene ferromagnetic
Researchers have developed a new approach for producing ferromagnetic amorphous GO. This involves introducing oxygen-containing functional groups and carbon defects into graphene, which modifies its electronic structure. After modifying the structure, the material is subjected to a self-assembly process in a supercritical carbon dioxide (SC CO2) environment. SC CO2 has properties that allow it to penetrate the graphene structure. The amorphous GO synthesized through this method exhibits high saturation magnetism and remanent magnetization at room temperature.
The process begins with forming graphene nanosheets, which are treated with SC CO2 in the presence of hydrogen peroxide (H2O2). This exposure facilitates the introduction of oxygen-containing functional groups and carbon defects, leading to the amorphization of the graphene structure.
“In addition to the well-established C vacancies and oxygen-containing groups for local magnetic moment and ferromagnetism, experimental and theoretical investigations suggest the out-of-plane oxygen-containing groups connect the graphene layers, leading to a sublattice imbalance structure with a significantly enhanced net magnetic moment,” said Qun Xu, a professor at Zhengzhou University in China and author of the research paper.
Referring to Figure 1, the impact of the interlayer adhesion on magnetism can be understood. The carbon vacancies and oxygen-containing groups are distributed randomly in the layers without adhesion, leading to small spin polarization. However, when these layers are interconnected via oxygen bridges, there’s a substantial increase in spin polarization. The adhesion tends to occur more frequently between carbon atoms of the A(A’) sublattice. This is due to the smaller distance between adjacent A-A’ sites than B-B’ sites.
Theoretical studies have shown that the out-of-plane oxygen-containing groups connect adjacent graphene layers. This causes sublattice imbalance and enhances net magnetic moments. Applying local pressure by SC CO2 is essential for overcoming the energy barrier to bridge the adjacent graphene layers, which induces the sublattice imbalance of the C atoms and improves the ferromagnetic states.
“Both experimental and theoretical studies have shown that SC CO2 plays a key role in the generation of ferromagnetism by exfoliating graphene, producing defects, introducing oxygen-containing functional groups and facilitating graphene layer adhesion,” researchers said.
Outlook for ferromagnetic graphene
One key aspect of this research is that the team did not rely on metals to induce magnetism in graphene. In some previous studies, researchers have embedded isolated cobalt atoms into graphene lattices with the assistance of coordinated N atoms. This effort to go metal-free to induce room-temperature ferromagnetism supports a sustainable future.
Achieving ferromagnetism in graphene is crucial because it enables control over electron spins, facilitating information storage and processing. This creates spin-polarized currents, a requirement for spintronic devices, such as spin transistors and magnetic memory.
Researchers say graphene is a promising candidate for the next generation of spintronics due to its extraordinary carrier mobility, long spin diffusion length, weak intrinsic spin-orbit coupling and limited hyperfine interactions.
The development of ferromagnetic graphene could lead to new magnetic devices that are smaller and more energy-efficient than their traditional counterparts. Such advancements hold the potential to transform the physics of spintronics.
References
1Zhang et al. (February 2024). “Room-Temperature Macroscopic Ferromagnetism in Multilayered Graphene Oxide.” Advanced Physics Research, 2300092.
2Han et al. (October 2014). “Graphene spintronics.” Nature Nanotechnology, 9, pp. 794–807.
3Hu et al. (March 2021). “Embedding atomic cobalt into graphene lattices to activate room-temperature ferromagnetism.” Nature Communications, 12.
4Maassen, J., Ji, W., & Guo, H. (December 2010). “Graphene Spintronics: The Role of Ferromagnetic Electrodes.” Nano Letters 11(1), pp. 151–155.
The post Ferromagnetism in Graphene at Room Temperature appeared first on Power Electronics News.
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