Rational design of a two-dimensional high-temperature ferromagnet from HCP cobalt.

Cobalt has the highest Curie temperature () among the elemental ferromagnetic metals and has a hexagonal close-packed (HCP) structure at room temperature. In this study, HCP Co was thinned to the thickness of several () unit cells along the -axis and then passivated by halogen atoms, thus being named CoX (X = F, Cl, Br and I). For CoX and CoX, all of them are not only kinetically but also thermodynamically stable from the viewpoint of the phonon spectra and molecular dynamics.