Half-Metals Enter Flatland
Half-metals are materials that conduct electricity using electrons of just one spin type: either spin up or spin down. A practical half-metal would help scientists realize energy-efficient spintronic technologies, devices that process and store data by harnessing both the charge and the spin of electrons. Unfortunately, the half-metals found so far operate only at cryogenic temperatures. What’s more, their half-metallicity fades at their surfaces, forestalling miniaturization. A 2D half-metal would be ideal. But although such a material has been predicted, it has not yet been produced. Now Xin Liang Tan of the Forschungszentrum Jülich, Germany, and his colleagues have engineered a 2D half-metal in the form of an ultrathin alloy of iron and palladium [1].
The team sought to induce half-metallicity through the complex interplay of two effects. The first is the exchange interaction, which causes the spins of neighboring electrons to align parallel to each other. The second is spin–orbit coupling, whereby an electron’s spin is linked to its orbital motion. Iron exhibits a strong exchange interaction, whereas palladium possesses a substantial spin–orbit coupling. Tan and his colleagues grew a two-atom-thick alloy of these two metals on the surface of a palladium crystal.
Using a state-of-the-art imaging technique called spin-resolved momentum microscopy, the researchers probed the alloy’s electronic structure. They found that the alloy’s electrons all had the same spin orientation at the Fermi energy, the energy relevant to conduction. This observation provides direct evidence for 2D half-metallicity, which the team backed up with theoretical modeling. Crucially, the alloy is disordered; its half-metallicity does not require crystalline perfection. These results overturn the conventional view that spin–orbit coupling is detrimental to half-metallicity and open a new route for finding spintronic materials.
–Ryan Wilkinson
Ryan Wilkinson is a Corresponding Editor for Physics Magazine based in Durham, UK.
References
- X. L. Tan et al., “Exchange engineering of a two-dimensional half-metal,” Phys. Rev. Lett. 135, 036703 (2025).