The electric, magnetic, physical or chemical properties of a 3D material can radically change when it's reduced to two dimensions – graphene, the versatile 2D form of graphite, is probably the best example. Now, researchers at the University of Washington and MIT have found the first material that retains magnetism in its 2D form, potentially opening the door to thinner electronics.
As the thinnest they can possibly be, materials just one atom thick are considered functionally two-dimensional. Unlike in a 3D atomic structure, electrons in these monolayers can only move around horizontally, which can have a major effect on a material's properties, such as how well it conducts electricity or how magnetic it is. As a result, magnetic materials tend to lose their magnetism when they're converted to a single layer.
But now, the team has isolated the first material that bucks the trend. Chromium triiodide (Crl3) is ferromagnetic, meaning it gets its magnetism through the symmetrical spin of its electrons, and the researchers found that even when shaved into a one-atom-thick monolayer, Crl3 maintained that magnetism.
They tested this by shining polarized light on the material, which returns a distinct signature in response to ferromagnetism. A single layer reflected the expected signature, but strangely, when stacked two layers high, the material lost its magnetic mojo. A third layer brought it back again, which raises some interesting questions about what's going on in that microscopic world.
"2D monolayers alone offer exciting opportunities to study the drastic and precise electrical control of magnetic properties, which has been a challenge to realize using their 3D bulk crystals," says Xiaodong Xu, lead author of the study. "But an even greater opportunity can arise when you stack monolayers with different physical properties together. There, you can get even more exotic phenomena not seen in the monolayer alone or in the 3D bulk crystal."
As with graphene, two-dimensional Crl3 could have some exciting applications in the ever-shrinking world of electronics.
"What we have discovered here is an isolated 2-D material with intrinsic magnetism, and the magnetism in the system is highly robust," says Xu. "We envision that new information technologies may emerge based on these new 2-D magnets."
The study was published in the journal Nature.
Source: University of Washington