Ferromagnetism versus antiferromagnetism of the Cr(001) surface

Three different spin arrangements for the (001) surface of Cr are discussed on the basis of self-consistent total-energy calculations: ferromagnetism, inside-the-surface $c(2\mathrm{}\times 2)$ antiferromagnetism, and "topological" antiferromagnetism between ferromagnetic terraces separated by single steps. The $c(2\mathrm{}\times 2)$ antiferromagnetic configuration is found to be energetically unfavorable. Instead, topological antiferromagnetism is compatible with both the absence of magnetization observed by spin-resolved photoemission and the existence of spin-split surface states detected by energy- and angular-resolved photoemission.