Ab initio calculations of incommensurate antiferromagnetic spin fluctuations in hcp iron under pressure -: art. no. 180405

We present ab initio calculations of the static paramagnetic spin susceptibility for hcp iron at finite temperatures and for a range of pressures. The dominant magnetic fluctuations in hcp Fe are found to be incommensurate antiferromagnetic, characterized by the wave vector q(inc) = (0.56,0.22,0). We show that q(inc) is linked to a Fermi-surface nesting feature. For the lowest pressure similar to16 GPa at which hcp Fe forms, we find that these modes become unstable below a Neel temperature (T-N) of 69 K. T-N rapidly diminishes with increasing pressure. We therefore predict that hcp Fe will be found to have an incommensurate spin-density-wave-ordered state over a small pressure range starting with the onset of hcp phase. We note the coincidence with the superconductivity recently found in this material.