From childhood we are taught that the world exists in three physical dimensions. That’s true for the most part, but it skips something very fascinating: the strange two-dimensional world of nanoscale materials, such as the “wonder material” graphene.
Graphene and its engineered, single-layer counterparts actually exist in three dimensions, albeit barely – sitting on the edge, atomically speaking. That’s because these so-called 2D materials are just one atom thick and embody incredible structural thinness that gives them all sorts of weird powers.
We see this in the formidable power of graphene, and in the way it approaches superconductivity.
It gets even stranger when graphene makes friends: Sheets of this two-dimensional material stack up into a three-layer sandwich of three atoms and a rare form of magnetism is revealed.
Now, in a new study led by physicists from the University of Cambridge, scientists have delivered the same kind of magnetic performance with another two-dimensional material called iron phosphorus trisulfide (FePS3).
(Cambridge University)
Above: Illustration of the magnetic structure of iron phosphorus trisulfide (FePS3), a two-dimensional material that undergoes a transition from an insulator to a metal when compressed.
FePS3 is not the same as graphene – which is composed of a single layer of carbon atoms – but it is often referred to as “magnetic graphene” because of its mysterious properties at ultra-thin, layered dimensions.
In an earlier study by some of the same researchers, the team found this when flattening layers of FePS3 were subjected to high pressure levels, where the material passed from an insulator, obstructing electron flow, to a metallic state where it became a conductor.
But researchers still did not fully understand what underlies the magnetic behavior of this ‘magnetic graphene’ under pressure, as FePS was expected to3 would cease to be magnetic when it enters the metallic state.
“The missing piece, however, has remained magnetism,” says quantum physicist Matthew Coak.
“Since there were no experimental techniques to investigate the characteristics 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.”
According to the new research, FePS3 maintains its magnetism under extremely high pressure by a newly discovered kind of magnetism that still exists during the metallic phase.
“To our surprise, we found that the magnetism survives and in some ways is enhanced,” explains senior researcher and physicist Siddharth Saxena, group leader at Cavendish Laboratory in Cambridge.
“This is unexpected, as the newly free-roaming electrons in a new conductive material can no longer be locked to their mother iron atoms, and generate magnetic moments there – unless the conduction comes from an unexpected source.”
While we don’t yet have all the answers as to what’s happening here, during compression the ‘spin’ of the electrons in the material seems to be a source of magnetism – and the phenomenon can be tuned depending on how much pressure FePS3 is subject to.
While the results contradict previous observations of how this material should behave, the surprises found here suggest we might be able to tweak magnetic graphene and its congeners even further – possibly finding materials that support superconductivity due to these exotic forms of magnetism that we do not yet fully understand.
“We don’t know exactly what is happening at the quantum level, but at the same time we can manipulate it,” says Saxena.
“It’s like those famous ‘unknown unknowns’: we’ve opened a new door to properties of quantum information, but we don’t yet know what those properties might be.”
The findings are reported in Physical assessment X.