Origin of ferromagnetism and the design principle in phase-change magnetic materials

The intrinsic ferromagnetism (FM) in phase-change (PC) magnetic materials was studied by first-principle calculations and experiments. The doped Fe or other transition metals tend to substitute at the Sb site of Ge${}_{2}$Sb${}_{2}$Te${}_{5}$. An asymmetric coupling, between ${p}_{\mathrm{x}}$ and ${p}_{\mathrm{y}}$ rather than ${p}_{\mathrm{z}}$ states of Te and $d$ states of Fe, creates magnetic moments and holes in the $p$ band. The findings reveal a strong dependence of FM interaction on Fe-Fe pair distances and crystallographic orientation. A design principle with three criteria is proposed for exploring new PC magnetic materials.