“ Magnetic graphene ” forms a new type of magnetism

Researchers have identified a new form of magnetism in so-called magnetic graphene, which could pave the way for understanding superconductivity in this unusual type of material.

The researchers, led by the University of Cambridge, were able to monitor the conductivity and magnetism of iron thiophosphate (FePS₃), a two-dimensional material that undergoes a transition from an insulator to a metal when compressed. This class of magnetic materials offers new avenues for understanding the physics of new magnetic states and superconductivity.

Using new high-pressure techniques, the researchers showed what happens to magnetic graphene during the transition from insulation to conductor and in its unconventional metallic state, achieved only under conditions of ultra-high pressure. When the material becomes metallic, it remains magnetic, which is contrary to the previous results and provides clues to the operation of electrical conduction in the metallic phase. The newly discovered high pressure magnetic phase probably forms a precursor to superconductivity, so understanding its mechanisms is vital.

Their results, published in the journal Physical examination X, also suggest a way to design new materials to combine conduction and magnetic properties, which could be useful in the development of new technologies such as spintronics, which could transform the way computers process information.

The properties of matter can change drastically with the change in dimension. For example, graphene, carbon nanotubes, graphite, and diamond are all made of carbon atoms, but have very different properties due to their different structure and dimensionality.

“But imagine if you could also change all of these properties by adding magnetism,” said first author Dr Matthew Coak, jointly based at the Cavendish Lab in Cambridge and the University of Warwick. “A material that could be mechanically flexible and form a new kind of circuit for storing information and performing calculations. This is why these materials are so interesting, and because they drastically change their properties when put under pressure. so that we can control their behavior. “

In a previous study by Sebastian Haines of the Cavendish Laboratory in Cambridge and the Department of Earth Sciences, researchers established that the material becomes a metal at high pressure and described how the crystal structure and arrangement of atoms in the layers of this 2-D material change. through the transition.

“The missing piece however remained, the magnetism,” Coak said. “In the absence of experimental techniques capable of probing the signatures of magnetism in this material at such high pressures, our international team had to develop and test our own new techniques to make this possible.”

The researchers used new techniques to measure the magnetic structure up to record pressures, using diamond anvils and specially designed neutrons to act as a probe for magnetism. They were then able to follow the evolution of magnetism towards the metallic state.

“To our surprise, we found that the magnetism survives and is in some ways enhanced,” co-author Dr. Siddharth Saxena, group leader at the Cavendish Lab. “This is unexpected, because the newly free electrons in a newly conductive material can no longer be locked to their parent iron atoms, generating magnetic moments there – unless the conduction comes from an unexpected source.”

In their previous article, the researchers showed that these electrons were “frozen” in a sense. But when they made them sink or move, they started to interact more and more. Magnetism survives, but changes into new forms, giving rise to new quantum properties in a new type of magnetic metal.

The behavior of a material, whether it is a conductor or an insulator, is mainly based on the way in which electrons, or charge, move. However, the “spin” of electrons turned out to be the source of magnetism. The spin causes the electrons to behave a bit like tiny bar magnets and point in a certain way. Magnetism from the arrangement of electron spins is used in most memory devices: its exploitation and control is important for developing new technologies such as spintronics, which could transform the way computers process information.

“The combination of the two, charge and spin, is the key to the behavior of this material,” said co-author Dr David Jarvis of Institut Laue-Langevin, France, who carried out this work as a basis. of his doctorate. .RE. studies at the Cavendish laboratory. “The discovery of this type of quantum multifunctionality is another leap forward in the study of these materials.”

“We don’t know exactly what’s going on at the quantum level, but at the same time, we can manipulate it,” Saxena said. “It’s like those famous ‘unknown unknowns’: we’ve opened a new door to the properties of quantum information, but we don’t yet know what those properties might be.”

There are more potential chemical compounds to be synthesized than it would ever be possible to fully explore and characterize. But by carefully selecting and adjusting materials with special properties, it is possible to show the way towards the creation of compounds and systems, but without having to apply enormous amounts of pressure.

Additionally, gaining a fundamental understanding of phenomena such as low dimensional magnetism and superconductivity enables researchers to make the next leaps in materials science and engineering, with particular potential in energy efficiency, production and storage.

Regarding the case of magnetic graphene, the researchers then plan to continue the search for superconductivity within this unique material. “Now that we have an idea of ​​what happens to this material at high pressure, we can make predictions about what might happen if we try to adjust its properties by adding free electrons by compressing it further,” Coak said. .

“What we’re looking for is superconductivity,” said Saxena. “If we can find a magnetism-related type of superconductivity in a two-dimensional material, it could give us a chance to solve a problem that dates back decades.”