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How to induce magnetism in graphene

wallpapers Tech 2021-01-06
Graphene is a two-dimensional structure made of carbon, a material with excellent mechanical, electronic and optical properties. However, it does not seem to be suitable for magnetic applications. Empa's researchers, in collaboration with international partners, have successfully synthesized the unique nanographene predicted in the 1970s, which finally proves that very special forms of carbon have magnetic properties that can allow future spintronics applications.
 
Depending on the shape and orientation of their edges, graphene nanostructures (also called nanographene) can have very different properties-for example, they may exhibit conductive, semi-conductive or insulating behavior. But, so far, one of the attributes is elusive: magnetism. Empa researchers, together with colleagues from the Dresden University of Technology, Aalto University in Finland, the Max Planck Institute for Polymer Research in Mainz, and the University of Bern, successfully constructed nanographene with magnetism, which can become self-contained The decisive component of the spin reaction. Basic electronic equipment works at room temperature.
 
Graphene consists only of carbon atoms, but magnetic properties are hardly related to carbon. So how do carbon nanomaterials exhibit magnetism? To understand this, we need to have a deep understanding of the fields of chemistry and atomic physics.
 
The carbon atoms in graphene are arranged in a honeycomb structure. Each carbon atom has three adjacent carbon atoms, which form alternating single or double bonds. In a single bond, one electron in each atom-the so-called valence electron-combines with adjacent atoms; while in a double bond, each atom has two electrons participating. This alternate single and double bond representation of organic compounds is called Kekulé structure, named after the German chemist Augustug Kekulé, who first proposed one of the simplest representations of organic compounds, benzene. The rule here is that the direction of rotation (the so-called spin) of electron pairs residing on the same orbit must be different. This is the result of the Pauli exclusion principle of quantum mechanics.
 
"However, in certain structures made of hexagons, it is never possible to draw alternating patterns of single and double bonds that meet the bonding requirements of each carbon atom. As a result, in this structure, one or more The electrons are forced to remain unpaired and unable to form", Shantanu Mishra explained, he is studying new nanotech at the Empa nanotech surfaces laboratory led by Roman Fasel. Representation. This phenomenon in which electrons are involuntarily unpaired is called "topological frustration."
 
But what does this have to do with magnetism? The answer lies in the "spin" of the electron. The rotation of an electron around its own axis generates a tiny magnetic field, the magnetic moment. If, as usual, there are two electrons with opposite spins in the orbit of the atom, these magnetic fields will cancel each other out. However, if the electron is lonely in its orbit, the magnetic moment remains the same — and a measurable magnetic field is produced.
This alone is fascinating. But in order to be able to use the spin of an electron as a circuit element, another step is required. One answer may be a structure that looks like a bow tie under a scanning tunneling microscope.

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