Ramp Compressed Iron Oxide XAFS above 300 GPa*

Understanding various electronic and magnetic changes at high pressures in iron compounds is not only an important solid-state physics question but is crucial in describing Earth’s lower mantle. An x-ray absorption platform has been developed at the Laboratory for Laser Energetics to understand material properties of compressed samples by simultaneously measuring x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure (EXAFS). Iron compounds were quasi-ramp compressed and the pressure was determined using a velocity interferometry system for any reflector (VISAR) on the OMEGA-60 laser. This platform has measured XANES at the highest pressures to date by 100s of GPa. An analytic method to characterize temperature and density was developed and compared to FEFF and electronic structure calculations from ab initio molecular-dynamics simulations based on density function theory.