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"exec" writes:

Arthur T Knackerbracket has found the following story:

The number of 2D materials has exploded since the discovery of graphene in 2004. However, this menagerie of single-atom-thick semiconductors, insulators and superconductors has been missing a member — magnets. In fact, physicists weren't even sure that 2D magnets were possible, until now.

Researchers report the first truly 2D magnet, made of a compound called chromium triiodide, in a paper published on 7 June in Nature. The discovery could eventually lead to new data-storage devices and designs for quantum computers. For now, the 2D magnets will enable physicists to perform previously impossible experiments and test fundamental theories of magnetism.

Pablo Jarillo-Herrero, a condensed-matter physicist at the Massachusetts Institute of Technology in Cambridge, and Xiaodong Xu, an optoelectronics researcher at the University of Washington in Seattle, were searching for a 2D magnet separately before meeting in 2016. They decided to combine forces to investigate. "It's a matter of principle — there is a big thing missing," says Jarillo-Herrero.

Xu and Jarillo-Herrero worked with chromium triiodide because it's a crystal comprising stacked sheets that can be separated using the 'Scotch tape method': a way of making 2D materials by using adhesive tape to peel off ever thinner layers. The scientists were also attracted to the compound because of its magnetic properties.

Like refrigerator magnets, chromium triiodide is a ferromagnet, a material that generates a permanent magnetic field owing to the aligned spins of its electrons. Chromium triiodide is also anisotropic, meaning that its electrons have a preferred spin direction — in this case, perpendicular to the plane of the crystal. These fundamental properties made Xu and Jarillo-Herrero suspect that chromium triiodide would retain its magnetic characteristics when stripped down to a single layer of atoms. That's something other 2D materials can't do.

Jarillo-Herrero's group grew chromium triiodide crystals and flaked off single- and multi-layer sheets, while Xu's lab studied the samples using a sensitive magnetometer.

The team found that not only was a single atomic layer of chromium triiodide magnetic, but also that this property emerged at what is considered a relatively warm temperature: about –228 °C. They also discovered that a two-layered sheet of this material isn't magnetic, but when a third is added the substance becomes a ferromagnet again. The material remains magnetic if a fourth layer is added, but gains other properties the researchers say they're still investigating.

-- submitted from IRC

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