Physicists Identify New Form of Magnetism in “Magnetic Graphene”

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The high-pressure magnetic phase observed in iron trithiohypophosphate, a 2D material that changes from an insulator to a metal when compressed, likely forms a precursor to superconductivity.

The magnetic structure of FePS3. Image credit: Cavendish Laboratory.

Iron trithiohypophosphate (FePS3), or magnetic graphene, belongs to a family of materials called van der Waals materials.

First synthesized in the 1960s, this 2D material is similar to graphene and can be “exfoliated” in ultra-thin layers. Unlike graphene however, FePS3 is magnetic.

In 2018, Dr Siddharth Saxena of the Cavendish Laboratory and his colleagues established than FePS3 becomes a metal at high pressure, and describes how the crystal structure and arrangement of atoms in the layers of this material changes during the transition.

In the new study, the researchers used new techniques to measure magnetic structure up to record pressures, using diamond anvils and specially designed neutrons to act as the magnetism probe.

They were then able to follow the evolution of magnetism to the metallic state.

“To our surprise, we found that the magnetism survives and is in some ways enhanced,” Dr Saxena said.

“This is unexpected, because the newly roving 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 study, the scientists 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 a conductor or an insulator, is primarily based on the way electrons, or charge, move. However, the “spin” of electrons has been shown to be the source of magnetism. The spinning causes the electrons to behave like tiny magnetic bars and point in a certain way.

“The combination of the two, charge and spin, is the key to the behavior of this material,” said Dr. David Jarvis, researcher at the Laue-Langevin Institute.

“Finding this kind 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,” Dr 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.”

“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,” said the Dr Matthew Coak, researcher. at the Cavendish Laboratory and the University of Warwick.

“What we are looking for is superconductivity,” added Dr Saxena.

“If we can find a magnetism-related type of superconductivity in a 2D material, it could give us a chance to solve a problem that dates back decades.”

The results were published on February 5, 2021 in the journal Physical examination X.

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Matthew J. Coak et al. 2021. Emerging magnetic phases in the pressure-regulated van der Waals FePS antiferromagnetic3. Phys. Rev. X 11 (1): 011024; doi: 10.1103 / PhysRevX.11.011024


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