Non-collinear magnetism in iron at high pressures

Using a first-principles based, magnetic tight-binding total energy model, the magnetization energy and moments are computed for various ordered spin configurations in the high pressure polymorphs of iron (fcc, or γ-Fe, and hcp, or ϵ-Fe), as well as ferromagnetic bcc iron (α-Fe). For hcp an antiferromagnetic spin configuration is more stable than non-magnetic ϵ iron up to about 50 GPa. Accounting for magnetism yields better agreement with the experimental equation of state, in contrast to the non-magnetic equation of state, which is in poor agreement with experiment below 50 GPa. We also studied non-collinear magnetism in γ- and ϵ-Fe. In ϵ-Fe the non-collinear effects are quite small energetically; in its stability field the collinear afmII structure is more stable than all non-collinear structures we explored.