The structure of graphene, which is a “sheet” of carbon atoms of monatomic thickness, is quite simple, however, this conventionally two-dimensional material has a number of unique and amazing properties. Not so long ago, a group of scientists from Stanford University showed that graphene, deformed in a special way, can produce a magnetic field. But the most surprising thing about this is that this new and special form of magnetism previously existed only in theory.
The two-dimensional nature of graphene determines that the electrons in this material move only along two spatial coordinates, which determines a number of unusual properties of the material. Last year, researchers at the Massachusetts Institute of Technology, using this, turned graphene into a superconducting material by folding two graphene sheets together and twisting them in a special way.
A group from Stanford tried to repeat what was done by scientists from Massachusetts, but they found that when an electric current is passed through graphene and it undergoes deformation of a certain type and force, the material acquires magnetic properties and produces a magnetic field. This is not the first time that graphene has been artificially endowed with magnetic properties, but previously this was achieved by exposing the material to an external magnetic field, adding additives to the structure, or combining graphene with other magnetic materials.
The most interesting is that the magnetism of deformed graphene is not ferromagnetism, the most common type of magnetism that occurs due to synchronization of electron spins. Instead, magnetism arose due to the linear alignment of the orbital motion of electrons, which is known in science as orbital ferromagnetism. “This is the first example of orbital ferromagnetism known to science,” the researchers write, “But the most surprising is that, contrary to our expectations, we not only see the manifestation of the Hall effect in this case, but we see a rather powerful manifestation of this effect.”
In their experiments, scientists squeezed two layers of graphene between thin layers of boron nitride, also having a hexagonal crystal lattice. Then they began to rotate one of the layers of boron nitride, which led to the curvature of the entire structure as a whole and made it possible to preserve the double graphene “sandwich” in integrity. The deforming graphene rotation was stronger than previously done by scientists from Massachusetts who turned the sheet 1.1 degrees. Stanford scientists turned graphene by 1.2 degrees, and this seemingly insignificant difference was enough for the appearance of magnetism in the material.
The magnetic field produced by deformed graphene is very weak, it is a million times weaker than the field from a simple magnet for a refrigerator. However, even such a weak magnetic field can be very useful in some specific applications.
"A double layer of deformed graphene can be switched into a magnetic state and vice versa with a very small amount of energy, and its state can be easily read using electronics," the researchers write, "and the fact that the magnetic field of this material is not directed outward, "it will allow the magnetic bits to be packed very tightly, without fear of mutual interference. This, in turn, will make it possible in the future to obtain such a recording density of information that even now may seem like something from the category of science fiction."
Deformation, Twisting, Graphene, Structure, Magnetism, Magnetic, Field
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