First Monolayer Magnet Discovered
Nancy Ordman | June 09, 2017Breakthrough research has identified the first material—chromium triiodide, CrI3--that retains its intrinsic magnetic properties when formed in a single layer. The discovery unlocks the door to development of new 
Side view of the latest 2-D material. Credit: Efren Navarro-Moratalla/MITinformation technologies.
A diverse international team of scientists reported this achievement in the journal Nature. Lead researchers are Xiaodong Xu from the University of Washington and Pablo Jarillo-Herrero of MIT.
Until now, scientists have not found a material that retains magnetism in 2D form. “You simply cannot accurately predict what the electric, magnetic, physical or chemical properties of a 2D monolayer crystal will be based on the behavior of its 3D bulk counterpart,” said co-lead author and UW doctoral student Bevin Huang.
Chromium triiodide exhibits strong ferromagnetic properties in its 3D form. To obtain a 2D layer for experimentation, the research team borrowed a technique first used to obtain graphene: using Scotch tape to pull a single-atom layer from a larger 3D crystal.
The team tested for intrinsic magnetism by reflecting a beam of polarized light off the monolayer. A ferromagnetic material yields a particular signature when tested this way; the CrI3 monolayer displayed this signature.
However, a two-atom-thick CrI3 layer lost this optical property, indicating that electron spins lined up opposite to each other. This is known as anti-ferromagnetic ordering. Additional studies are necessary to figure out why these two forms have different electrical properties.
Xu is excited by the potential for controlling magnetic properties in 2D magnets. “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,” Xu said.
In addition to working with the CrI3 monolayer, Xu is interested in creating heterostructures—stacks of two different ultrathin materials—and looking for new physical phenomena or properties that can push information technology forward.
OK, so three atoms thick appears to work as a ferromagnetic layer, but two atoms thick, no dice. Run spectra on the two layer material, I bet it is no longer CrI3, but something entirely different, probably not pure substance. Would the electron paramagnetic spectrum tell you the oxidation state (assembly average) of the Chromium present?
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