Journal Article European XFEL soft X-rays Heisenberg RIXS RIXS Research Support, Non-U.S. Gov't X-ray Raman scattering X-ray resonant diffraction X-ray total scattering XFEL charge order diamond anvil cell extreme conditions free-electron lasers hRIXS high angular resolution high-energy X-rays high-pressure melting of iron holography magnetic X-ray scattering photochemistry pulse laser heating ray-tracing simulations resonant X-ray diffraction resonant inelastic X-ray scattering spin dynamics spin order synchrotron powder diffraction time-resolved experiments time-resolved spectroscopy