Iron under pressure: "Kohn tweezers" and remnant magnetism.

In this work we investigate the magnetic and structural properties of bulk Fe and Fe nanoparticles under pressure with x-ray absorption and emission spectroscopies providing answers to two fundamental questions: (a) the chicken-or-egg problem for the magnetic and structural transitions and (b) magnetism in the high pressure hcp phase. The two transitions, inextricably linked in the bulk, are clearly decoupled in the nanoparticles, with the magnetic collapse preceding the structural transition. Ultrafast x-ray emission spectroscopy detects remnant magnetism, probably antiferromagnetic fluctuations, up to pressures of about 40 GPa in the hcp phase. This could be of direct relevance to the superconductivity in ϵ-Fe [K. Shimizu et al., Nature (London) 412, 316 (2001)] through the existence of a quantum critical point and associated magnetic fluctuations.